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 $187.92   8.398%   $203.7015   $203.70   $203.70   $203.70  
  Purchase #2 $173.36   11.806%   $193.8269   $193.83   $193.85   $193.80  
  Purchase #3 $42.93   12.195%   $48.1653   $48.17   $48.15   $48.20  
  Purchase #4 $196.46   11.299%   $218.658   $218.66   $218.65   $218.70  
  Purchase #5 $21.52   8.626%   $23.3763   $23.38   $23.40   $23.40  
  Purchase #6 $197.95   8.874%   $215.5161   $215.52   $215.50   $215.50  
  Purchase #7 $77.91   8.214%   $84.3095   $84.31   $84.30   $84.30  
  7 purchase totals = $898.05       $987.5536   $987.57   $987.55   $987.60