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 $243.30   9.746%   $267.012   $267.01   $267.00   $267.00  
  Purchase #2 $22.42   12.534%   $25.2301   $25.23   $25.25   $25.20  
  Purchase #3 $158.77   6.672%   $169.3631   $169.36   $169.35   $169.40  
  Purchase #4 $56.66   4.712%   $59.3298   $59.33   $59.35   $59.30  
  Purchase #5 $62.68   5.805%   $66.3186   $66.32   $66.30   $66.30  
  Purchase #6 $27.54   5.874%   $29.1577   $29.16   $29.15   $29.20  
  Purchase #7 $132.59   8.719%   $144.1505   $144.15   $144.15   $144.20  
  7 purchase totals = $703.96       $760.5618   $760.56   $760.55   $760.60