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 $136.93   12.211%   $153.6505   $153.65   $153.65   $153.70  
  Purchase #2 $60.37   6.676%   $64.4003   $64.40   $64.40   $64.40  
  Purchase #3 $211.90   6.717%   $226.1333   $226.13   $226.15   $226.10  
  Purchase #4 $241.85   6.679%   $258.0032   $258.00   $258.00   $258.00  
  Purchase #5 $184.72   9.778%   $202.7819   $202.78   $202.80   $202.80  
  Purchase #6 $238.33   8.787%   $259.2721   $259.27   $259.25   $259.30  
  Purchase #7 $177.59   3.464%   $183.7417   $183.74   $183.75   $183.70  
  7 purchase totals = $1,251.69       $1,347.9830   $1,347.97   $1,348.00   $1,348.00