Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $203.51   13.181%   $230.3347   $230.33   $230.35   $230.30  
  Purchase #2 $206.97   9.649%   $226.9405   $226.94   $226.95   $226.90  
  Purchase #3 $152.89   10.669%   $169.2018   $169.20   $169.20   $169.20  
  Purchase #4 $217.67   12.514%   $244.9092   $244.91   $244.90   $244.90  
  Purchase #5 $177.33   3.385%   $183.3326   $183.33   $183.35   $183.30  
  Purchase #6 $196.30   10.111%   $216.1479   $216.15   $216.15   $216.10  
  Purchase #7 $169.31   11.571%   $188.9009   $188.90   $188.90   $188.90  
  7 purchase totals = $1,323.98       $1,459.7676   $1,459.76   $1,459.80   $1,459.60