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 $67.44   9.352%   $73.747   $73.75   $73.75   $73.70  
  Purchase #2 $56.71   13.468%   $64.3477   $64.35   $64.35   $64.30  
  Purchase #3 $66.77   13.339%   $75.6765   $75.68   $75.70   $75.70  
  Purchase #4 $222.97   12.606%   $251.0776   $251.08   $251.10   $251.10  
  Purchase #5 $151.66   6.142%   $160.975   $160.98   $161.00   $161.00  
  Purchase #6 $246.51   8.869%   $268.373   $268.37   $268.35   $268.40  
  Purchase #7 $20.91   7.411%   $22.4596   $22.46   $22.45   $22.50  
  7 purchase totals = $832.97       $916.6564   $916.67   $916.70   $916.70