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 $146.79   11.254%   $163.3097   $163.31   $163.30   $163.30  
  Purchase #2 $9.93   8.640%   $10.788   $10.79   $10.80   $10.80  
  Purchase #3 $171.96   11.852%   $192.3407   $192.34   $192.35   $192.30  
  Purchase #4 $59.75   8.421%   $64.7815   $64.78   $64.80   $64.80  
  Purchase #5 $126.70   8.213%   $137.1059   $137.11   $137.10   $137.10  
  Purchase #6 $160.73   5.394%   $169.3998   $169.40   $169.40   $169.40  
  Purchase #7 $14.90   10.695%   $16.4936   $16.49   $16.50   $16.50  
  7 purchase totals = $690.76       $754.2192   $754.22   $754.25   $754.20