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 $56.43   3.804%   $58.5766   $58.58   $58.60   $58.60  
  Purchase #2 $22.90   9.490%   $25.0732   $25.07   $25.05   $25.10  
  Purchase #3 $166.27   7.372%   $178.5274   $178.53   $178.55   $178.50  
  Purchase #4 $210.95   13.222%   $238.8418   $238.84   $238.85   $238.80  
  Purchase #5 $31.98   5.804%   $33.8361   $33.84   $33.85   $33.80  
  Purchase #6 $201.87   7.209%   $216.4228   $216.42   $216.40   $216.40  
  Purchase #7 $248.68   3.210%   $256.6626   $256.66   $256.65   $256.70  
  7 purchase totals = $939.08       $1,007.9405   $1,007.94   $1,007.95   $1,007.90