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 $184.82   10.182%   $203.6384   $203.64   $203.65   $203.60  
  Purchase #2 $88.47   4.708%   $92.6352   $92.64   $92.65   $92.60  
  Purchase #3 $31.85   13.655%   $36.1991   $36.20   $36.20   $36.20  
  Purchase #4 $231.51   4.223%   $241.2867   $241.29   $241.30   $241.30  
  Purchase #5 $40.34   10.403%   $44.5366   $44.54   $44.55   $44.50  
  Purchase #6 $146.49   4.493%   $153.0718   $153.07   $153.05   $153.10  
  Purchase #7 $30.38   6.472%   $32.3462   $32.35   $32.35   $32.30  
  7 purchase totals = $753.86       $803.7140   $803.73   $803.75   $803.60