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 $127.51   10.746%   $141.2122   $141.21   $141.20   $141.20  
  Purchase #2 $144.50   11.378%   $160.9412   $160.94   $160.95   $160.90  
  Purchase #3 $117.39   8.128%   $126.9315   $126.93   $126.95   $126.90  
  Purchase #4 $141.81   3.324%   $146.5238   $146.52   $146.50   $146.50  
  Purchase #5 $233.54   11.413%   $260.1939   $260.19   $260.20   $260.20  
  Purchase #6 $188.94   6.733%   $201.6613   $201.66   $201.65   $201.70  
  Purchase #7 $89.96   4.521%   $94.0271   $94.03   $94.05   $94.00  
  7 purchase totals = $1,043.65       $1,131.4910   $1,131.48   $1,131.50   $1,131.40