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 $61.80   10.467%   $68.2686   $68.27   $68.25   $68.30  
  Purchase #2 $160.83   9.282%   $175.7582   $175.76   $175.75   $175.80  
  Purchase #3 $86.98   6.139%   $92.3197   $92.32   $92.30   $92.30  
  Purchase #4 $79.72   9.860%   $87.5804   $87.58   $87.60   $87.60  
  Purchase #5 $102.42   4.443%   $106.9705   $106.97   $106.95   $107.00  
  Purchase #6 $104.79   10.739%   $116.0434   $116.04   $116.05   $116.00  
  Purchase #7 $250.64   6.541%   $267.0344   $267.03   $267.05   $267.00  
  7 purchase totals = $847.18       $913.9752   $913.97   $913.95   $914.00