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 $54.55   13.490%   $61.9088   $61.91   $61.90   $61.90  
  Purchase #2 $20.55   5.357%   $21.6509   $21.65   $21.65   $21.70  
  Purchase #3 $91.92   12.377%   $103.2969   $103.30   $103.30   $103.30  
  Purchase #4 $113.34   11.322%   $126.1724   $126.17   $126.15   $126.20  
  Purchase #5 $43.63   7.746%   $47.0096   $47.01   $47.00   $47.00  
  Purchase #6 $181.38   13.477%   $205.8246   $205.82   $205.80   $205.80  
  Purchase #7 $174.57   11.699%   $194.9929   $194.99   $195.00   $195.00  
  7 purchase totals = $679.94       $760.8561   $760.85   $760.80   $760.90