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 $244.67   8.520%   $265.5159   $265.52   $265.50   $265.50  
  Purchase #2 $166.73   10.495%   $184.2283   $184.23   $184.25   $184.20  
  Purchase #3 $30.34   11.436%   $33.8097   $33.81   $33.80   $33.80  
  Purchase #4 $116.41   11.651%   $129.9729   $129.97   $129.95   $130.00  
  Purchase #5 $58.99   3.755%   $61.2051   $61.21   $61.20   $61.20  
  Purchase #6 $97.49   10.607%   $107.8308   $107.83   $107.85   $107.80  
  Purchase #7 $103.52   8.777%   $112.606   $112.61   $112.60   $112.60  
  7 purchase totals = $818.15       $895.1687   $895.18   $895.15   $895.10