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 $184.87   10.104%   $203.5493   $203.55   $203.55   $203.50  
  Purchase #2 $146.33   9.200%   $159.7924   $159.79   $159.80   $159.80  
  Purchase #3 $185.49   11.169%   $206.2074   $206.21   $206.20   $206.20  
  Purchase #4 $210.64   4.370%   $219.845   $219.85   $219.85   $219.80  
  Purchase #5 $17.64   5.478%   $18.6063   $18.61   $18.60   $18.60  
  Purchase #6 $104.87   13.471%   $118.997   $119.00   $119.00   $119.00  
  Purchase #7 $113.61   8.237%   $122.9681   $122.97   $122.95   $123.00  
  7 purchase totals = $963.45       $1,049.9655   $1,049.98   $1,049.95   $1,049.90