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 $87.59   7.286%   $93.9718   $93.97   $93.95   $94.00  
  Purchase #2 $133.69   5.456%   $140.9841   $140.98   $141.00   $141.00  
  Purchase #3 $205.82   5.686%   $217.5229   $217.52   $217.50   $217.50  
  Purchase #4 $56.93   4.148%   $59.2915   $59.29   $59.30   $59.30  
  Purchase #5 $43.57   12.645%   $49.0794   $49.08   $49.10   $49.10  
  Purchase #6 $30.77   10.328%   $33.9479   $33.95   $33.95   $33.90  
  Purchase #7 $165.47   3.282%   $170.9007   $170.90   $170.90   $170.90  
  7 purchase totals = $723.84       $765.6983   $765.69   $765.70   $765.70