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 $72.37   4.757%   $75.8126   $75.81   $75.80   $75.80  
  Purchase #2 $166.59   10.763%   $184.5201   $184.52   $184.50   $184.50  
  Purchase #3 $188.96   10.825%   $209.4149   $209.41   $209.40   $209.40  
  Purchase #4 $77.95   8.378%   $84.4807   $84.48   $84.50   $84.50  
  Purchase #5 $55.57   11.364%   $61.885   $61.89   $61.90   $61.90  
  Purchase #6 $145.31   4.302%   $151.5612   $151.56   $151.55   $151.60  
  Purchase #7 $114.78   12.874%   $129.5568   $129.56   $129.55   $129.60  
  7 purchase totals = $821.53       $897.2313   $897.23   $897.20   $897.30