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 $184.43   9.657%   $202.2404   $202.24   $202.25   $202.20  
  Purchase #2 $148.84   12.669%   $167.6965   $167.70   $167.70   $167.70  
  Purchase #3 $16.56   13.125%   $18.7335   $18.73   $18.75   $18.70  
  Purchase #4 $111.35   9.367%   $121.7802   $121.78   $121.80   $121.80  
  Purchase #5 $18.58   5.523%   $19.6062   $19.61   $19.60   $19.60  
  Purchase #6 $49.41   10.674%   $54.684   $54.68   $54.70   $54.70  
  Purchase #7 $126.56   5.472%   $133.4854   $133.49   $133.50   $133.50  
  7 purchase totals = $655.73       $718.2262   $718.23   $718.30   $718.20