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 $7.44   4.283%   $7.7587   $7.76   $7.75   $7.80  
  Purchase #2 $9.41   7.129%   $10.0808   $10.08   $10.10   $10.10  
  Purchase #3 $99.84   10.179%   $110.0027   $110.00   $110.00   $110.00  
  Purchase #4 $157.62   7.427%   $169.3264   $169.33   $169.35   $169.30  
  Purchase #5 $134.80   4.412%   $140.7474   $140.75   $140.75   $140.70  
  Purchase #6 $202.54   12.550%   $227.9588   $227.96   $227.95   $228.00  
  Purchase #7 $200.92   13.548%   $228.1406   $228.14   $228.15   $228.10  
  7 purchase totals = $812.57       $894.0154   $894.02   $894.05   $894.00