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 $197.41   4.486%   $206.2658   $206.27   $206.25   $206.30  
  Purchase #2 $73.38   8.163%   $79.37   $79.37   $79.35   $79.40  
  Purchase #3 $118.53   10.140%   $130.5489   $130.55   $130.55   $130.50  
  Purchase #4 $31.61   3.155%   $32.6073   $32.61   $32.60   $32.60  
  Purchase #5 $128.66   13.270%   $145.7332   $145.73   $145.75   $145.70  
  Purchase #6 $119.69   4.794%   $125.4279   $125.43   $125.45   $125.40  
  Purchase #7 $210.60   13.131%   $238.2539   $238.25   $238.25   $238.30  
  7 purchase totals = $879.88       $958.2070   $958.21   $958.20   $958.20