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 $125.87   5.846%   $133.2284   $133.23   $133.25   $133.20  
  Purchase #2 $75.75   8.699%   $82.3395   $82.34   $82.35   $82.30  
  Purchase #3 $123.63   5.234%   $130.1008   $130.10   $130.10   $130.10  
  Purchase #4 $171.36   5.342%   $180.5141   $180.51   $180.50   $180.50  
  Purchase #5 $52.29   3.740%   $54.2456   $54.25   $54.25   $54.20  
  Purchase #6 $152.36   10.657%   $168.597   $168.60   $168.60   $168.60  
  Purchase #7 $243.95   10.149%   $268.7085   $268.71   $268.70   $268.70  
  7 purchase totals = $945.21       $1,017.7339   $1,017.74   $1,017.75   $1,017.60