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 $59.68   13.463%   $67.7147   $67.71   $67.70   $67.70  
  Purchase #2 $33.49   6.578%   $35.693   $35.69   $35.70   $35.70  
  Purchase #3 $61.44   8.665%   $66.7638   $66.76   $66.75   $66.80  
  Purchase #4 $208.35   12.342%   $234.0646   $234.06   $234.05   $234.10  
  Purchase #5 $102.31   4.872%   $107.2945   $107.29   $107.30   $107.30  
  Purchase #6 $87.94   3.598%   $91.1041   $91.10   $91.10   $91.10  
  Purchase #7 $229.35   10.519%   $253.4753   $253.48   $253.50   $253.50  
  7 purchase totals = $782.56       $856.1100   $856.09   $856.10   $856.20