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 $223.72   4.128%   $232.9552   $232.96   $232.95   $233.00  
  Purchase #2 $36.84   11.300%   $41.0029   $41.00   $41.00   $41.00  
  Purchase #3 $170.28   11.259%   $189.4518   $189.45   $189.45   $189.50  
  Purchase #4 $63.57   13.169%   $71.9415   $71.94   $71.95   $71.90  
  Purchase #5 $69.72   8.583%   $75.7041   $75.70   $75.70   $75.70  
  Purchase #6 $178.79   11.432%   $199.2293   $199.23   $199.25   $199.20  
  Purchase #7 $123.34   10.831%   $136.699   $136.70   $136.70   $136.70  
  7 purchase totals = $866.26       $946.9838   $946.98   $947.00   $947.00