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 $242.39   12.647%   $273.0451   $273.05   $273.05   $273.00  
  Purchase #2 $131.51   13.788%   $149.6426   $149.64   $149.65   $149.60  
  Purchase #3 $81.62   7.723%   $87.9235   $87.92   $87.90   $87.90  
  Purchase #4 $188.47   12.609%   $212.2342   $212.23   $212.25   $212.20  
  Purchase #5 $32.34   6.776%   $34.5314   $34.53   $34.55   $34.50  
  Purchase #6 $44.40   4.152%   $46.2435   $46.24   $46.25   $46.20  
  Purchase #7 $230.49   6.457%   $245.3727   $245.37   $245.35   $245.40  
  7 purchase totals = $951.22       $1,048.9930   $1,048.98   $1,049.00   $1,048.80