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 $186.74   10.223%   $205.8304   $205.83   $205.85   $205.80  
  Purchase #2 $144.34   7.380%   $154.9923   $154.99   $155.00   $155.00  
  Purchase #3 $14.59   13.795%   $16.6027   $16.60   $16.60   $16.60  
  Purchase #4 $236.77   7.109%   $253.602   $253.60   $253.60   $253.60  
  Purchase #5 $63.33   3.107%   $65.2977   $65.30   $65.30   $65.30  
  Purchase #6 $186.98   12.256%   $209.8963   $209.90   $209.90   $209.90  
  Purchase #7 $164.43   8.215%   $177.9379   $177.94   $177.95   $177.90  
  7 purchase totals = $997.18       $1,084.1593   $1,084.16   $1,084.20   $1,084.10