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 $56.53   9.276%   $61.7737   $61.77   $61.75   $61.80  
  Purchase #2 $220.38   13.455%   $250.0321   $250.03   $250.05   $250.00  
  Purchase #3 $63.38   10.325%   $69.924   $69.92   $69.90   $69.90  
  Purchase #4 $31.76   10.244%   $35.0135   $35.01   $35.00   $35.00  
  Purchase #5 $107.36   13.168%   $121.4972   $121.50   $121.50   $121.50  
  Purchase #6 $140.58   13.750%   $159.9098   $159.91   $159.90   $159.90  
  Purchase #7 $189.33   3.290%   $195.559   $195.56   $195.55   $195.60  
  7 purchase totals = $809.32       $893.7093   $893.70   $893.65   $893.70