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 $225.47   12.417%   $253.4666   $253.47   $253.45   $253.50  
  Purchase #2 $71.47   3.347%   $73.8621   $73.86   $73.85   $73.90  
  Purchase #3 $101.58   12.470%   $114.247   $114.25   $114.25   $114.20  
  Purchase #4 $62.25   4.339%   $64.951   $64.95   $64.95   $65.00  
  Purchase #5 $160.29   11.847%   $179.2796   $179.28   $179.30   $179.30  
  Purchase #6 $28.49   9.503%   $31.1974   $31.20   $31.20   $31.20  
  Purchase #7 $49.84   12.278%   $55.9594   $55.96   $55.95   $56.00  
  7 purchase totals = $699.39       $772.9631   $772.97   $772.95   $773.10