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 $232.76   13.292%   $263.6985   $263.70   $263.70   $263.70  
  Purchase #2 $34.37   8.574%   $37.3169   $37.32   $37.30   $37.30  
  Purchase #3 $129.44   12.606%   $145.7572   $145.76   $145.75   $145.80  
  Purchase #4 $188.62   3.401%   $195.035   $195.04   $195.05   $195.00  
  Purchase #5 $162.37   5.273%   $170.9318   $170.93   $170.95   $170.90  
  Purchase #6 $169.65   13.666%   $192.8344   $192.83   $192.85   $192.80  
  Purchase #7 $206.91   11.268%   $230.2246   $230.22   $230.20   $230.20  
  7 purchase totals = $1,124.12       $1,235.7984   $1,235.80   $1,235.80   $1,235.70