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 $146.76   11.366%   $163.4407   $163.44   $163.45   $163.40  
  Purchase #2 $61.52   11.136%   $68.3709   $68.37   $68.35   $68.40  
  Purchase #3 $178.37   13.780%   $202.9494   $202.95   $202.95   $202.90  
  Purchase #4 $153.31   3.672%   $158.9395   $158.94   $158.95   $158.90  
  Purchase #5 $68.34   9.718%   $74.9813   $74.98   $75.00   $75.00  
  Purchase #6 $198.25   5.513%   $209.1795   $209.18   $209.20   $209.20  
  Purchase #7 $135.81   5.509%   $143.2918   $143.29   $143.30   $143.30  
  7 purchase totals = $942.36       $1,021.1531   $1,021.15   $1,021.20   $1,021.10