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 $233.74   8.441%   $253.47   $253.47   $253.45   $253.50  
  Purchase #2 $60.49   7.540%   $65.0509   $65.05   $65.05   $65.10  
  Purchase #3 $107.45   10.713%   $118.9611   $118.96   $118.95   $119.00  
  Purchase #4 $179.82   9.624%   $197.1259   $197.13   $197.15   $197.10  
  Purchase #5 $229.29   9.179%   $250.3365   $250.34   $250.35   $250.30  
  Purchase #6 $141.82   3.424%   $146.6759   $146.68   $146.70   $146.70  
  Purchase #7 $32.59   13.276%   $36.9166   $36.92   $36.90   $36.90  
  7 purchase totals = $985.20       $1,068.5369   $1,068.55   $1,068.55   $1,068.60