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 $119.26   12.378%   $134.022   $134.02   $134.00   $134.00  
  Purchase #2 $32.30   10.427%   $35.6679   $35.67   $35.65   $35.70  
  Purchase #3 $151.42   12.791%   $170.7881   $170.79   $170.80   $170.80  
  Purchase #4 $44.68   6.542%   $47.603   $47.60   $47.60   $47.60  
  Purchase #5 $154.99   6.512%   $165.0829   $165.08   $165.10   $165.10  
  Purchase #6 $237.83   3.853%   $246.9936   $246.99   $247.00   $247.00  
  Purchase #7 $88.33   9.759%   $96.9501   $96.95   $96.95   $97.00  
  7 purchase totals = $828.81       $897.1076   $897.10   $897.10   $897.20