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 $145.44   8.318%   $157.5377   $157.54   $157.55   $157.50  
  Purchase #2 $60.44   4.116%   $62.9277   $62.93   $62.95   $62.90  
  Purchase #3 $18.32   6.630%   $19.5346   $19.53   $19.55   $19.50  
  Purchase #4 $104.79   5.152%   $110.1888   $110.19   $110.20   $110.20  
  Purchase #5 $47.33   11.336%   $52.6953   $52.70   $52.70   $52.70  
  Purchase #6 $29.49   10.402%   $32.5575   $32.56   $32.55   $32.60  
  Purchase #7 $153.89   11.648%   $171.8151   $171.82   $171.80   $171.80  
  7 purchase totals = $559.70       $607.2567   $607.27   $607.30   $607.20