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 $175.74   12.318%   $197.3877   $197.39   $197.40   $197.40  
  Purchase #2 $229.34   11.120%   $254.8426   $254.84   $254.85   $254.80  
  Purchase #3 $46.47   12.492%   $52.275   $52.28   $52.30   $52.30  
  Purchase #4 $173.35   3.458%   $179.3444   $179.34   $179.35   $179.30  
  Purchase #5 $125.85   5.653%   $132.9643   $132.96   $132.95   $133.00  
  Purchase #6 $157.98   8.252%   $171.0165   $171.02   $171.00   $171.00  
  Purchase #7 $26.51   6.857%   $28.3278   $28.33   $28.35   $28.30  
  7 purchase totals = $935.24       $1,016.1583   $1,016.16   $1,016.20   $1,016.10