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 $206.84   8.741%   $224.9199   $224.92   $224.90   $224.90  
  Purchase #2 $149.30   8.190%   $161.5277   $161.53   $161.55   $161.50  
  Purchase #3 $46.52   8.648%   $50.543   $50.54   $50.55   $50.50  
  Purchase #4 $59.54   5.832%   $63.0124   $63.01   $63.00   $63.00  
  Purchase #5 $235.62   13.485%   $267.3934   $267.39   $267.40   $267.40  
  Purchase #6 $118.98   11.209%   $132.3165   $132.32   $132.30   $132.30  
  Purchase #7 $219.74   6.672%   $234.4011   $234.40   $234.40   $234.40  
  7 purchase totals = $1,036.54       $1,134.1140   $1,134.11   $1,134.10   $1,134.00