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 $32.58   3.610%   $33.7561   $33.76   $33.75   $33.80  
  Purchase #2 $187.83   5.387%   $197.9484   $197.95   $197.95   $197.90  
  Purchase #3 $203.41   8.719%   $221.1453   $221.15   $221.15   $221.10  
  Purchase #4 $164.53   11.454%   $183.3753   $183.38   $183.40   $183.40  
  Purchase #5 $108.97   10.826%   $120.7671   $120.77   $120.75   $120.80  
  Purchase #6 $151.30   8.264%   $163.8034   $163.80   $163.80   $163.80  
  Purchase #7 $20.30   10.572%   $22.4461   $22.45   $22.45   $22.40  
  7 purchase totals = $868.92       $943.2417   $943.26   $943.25   $943.20