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 $87.78   11.240%   $97.6465   $97.65   $97.65   $97.60  
  Purchase #2 $178.37   10.559%   $197.2041   $197.20   $197.20   $197.20  
  Purchase #3 $91.25   11.497%   $101.741   $101.74   $101.75   $101.70  
  Purchase #4 $119.93   5.737%   $126.8104   $126.81   $126.80   $126.80  
  Purchase #5 $43.97   6.276%   $46.7296   $46.73   $46.75   $46.70  
  Purchase #6 $31.60   10.847%   $35.0277   $35.03   $35.05   $35.00  
  Purchase #7 $174.74   11.678%   $195.1461   $195.15   $195.15   $195.10  
  7 purchase totals = $727.64       $800.3054   $800.31   $800.35   $800.10