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 $208.53   11.727%   $232.9843   $232.98   $233.00   $233.00  
  Purchase #2 $170.37   13.866%   $193.9935   $193.99   $194.00   $194.00  
  Purchase #3 $69.93   4.856%   $73.3258   $73.33   $73.35   $73.30  
  Purchase #4 $189.62   10.494%   $209.5187   $209.52   $209.50   $209.50  
  Purchase #5 $69.97   4.874%   $73.3803   $73.38   $73.40   $73.40  
  Purchase #6 $222.33   10.690%   $246.0971   $246.10   $246.10   $246.10  
  Purchase #7 $163.28   10.176%   $179.8954   $179.90   $179.90   $179.90  
  7 purchase totals = $1,094.03       $1,209.1951   $1,209.20   $1,209.25   $1,209.20