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 $58.57   3.596%   $60.6762   $60.68   $60.70   $60.70  
  Purchase #2 $240.92   6.287%   $256.0666   $256.07   $256.05   $256.10  
  Purchase #3 $20.45   5.262%   $21.5261   $21.53   $21.55   $21.50  
  Purchase #4 $134.34   9.305%   $146.8403   $146.84   $146.85   $146.80  
  Purchase #5 $217.55   6.116%   $230.8554   $230.86   $230.85   $230.90  
  Purchase #6 $182.30   5.754%   $192.7895   $192.79   $192.80   $192.80  
  Purchase #7 $42.49   7.457%   $45.6585   $45.66   $45.65   $45.70  
  7 purchase totals = $896.62       $954.4126   $954.43   $954.45   $954.50