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 $211.56   13.133%   $239.3442   $239.34   $239.35   $239.30  
  Purchase #2 $125.56   8.299%   $135.9802   $135.98   $136.00   $136.00  
  Purchase #3 $79.58   10.505%   $87.9399   $87.94   $87.95   $87.90  
  Purchase #4 $88.54   9.227%   $96.7096   $96.71   $96.70   $96.70  
  Purchase #5 $195.68   5.295%   $206.0413   $206.04   $206.05   $206.00  
  Purchase #6 $121.38   8.281%   $131.4315   $131.43   $131.45   $131.40  
  Purchase #7 $182.89   11.549%   $204.012   $204.01   $204.00   $204.00  
  7 purchase totals = $1,005.19       $1,101.4587   $1,101.45   $1,101.50   $1,101.30