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 $128.37   6.755%   $137.0414   $137.04   $137.05   $137.00  
  Purchase #2 $187.62   4.361%   $195.8021   $195.80   $195.80   $195.80  
  Purchase #3 $206.43   5.786%   $218.374   $218.37   $218.35   $218.40  
  Purchase #4 $234.83   11.701%   $262.3075   $262.31   $262.30   $262.30  
  Purchase #5 $221.60   5.370%   $233.4999   $233.50   $233.50   $233.50  
  Purchase #6 $67.82   13.148%   $76.737   $76.74   $76.75   $76.70  
  Purchase #7 $232.88   9.583%   $255.1969   $255.20   $255.20   $255.20  
  7 purchase totals = $1,279.55       $1,378.9588   $1,378.96   $1,378.95   $1,378.90