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 $64.92   10.560%   $71.7756   $71.78   $71.80   $71.80  
  Purchase #2 $134.30   12.323%   $150.8498   $150.85   $150.85   $150.80  
  Purchase #3 $29.26   6.680%   $31.2146   $31.21   $31.20   $31.20  
  Purchase #4 $209.79   11.138%   $233.1564   $233.16   $233.15   $233.20  
  Purchase #5 $42.60   12.556%   $47.9489   $47.95   $47.95   $47.90  
  Purchase #6 $143.47   6.712%   $153.0997   $153.10   $153.10   $153.10  
  Purchase #7 $58.69   6.183%   $62.3188   $62.32   $62.30   $62.30  
  7 purchase totals = $683.03       $750.3638   $750.37   $750.35   $750.30