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 $48.68   8.257%   $52.6995   $52.70   $52.70   $52.70  
  Purchase #2 $188.88   10.707%   $209.1034   $209.10   $209.10   $209.10  
  Purchase #3 $83.99   5.104%   $88.2768   $88.28   $88.30   $88.30  
  Purchase #4 $221.42   7.394%   $237.7918   $237.79   $237.80   $237.80  
  Purchase #5 $108.98   10.648%   $120.5842   $120.58   $120.60   $120.60  
  Purchase #6 $163.95   8.739%   $178.2776   $178.28   $178.30   $178.30  
  Purchase #7 $154.58   12.427%   $173.7897   $173.79   $173.80   $173.80  
  7 purchase totals = $970.48       $1,060.5230   $1,060.52   $1,060.60   $1,060.60