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 $227.53   8.562%   $247.0111   $247.01   $247.00   $247.00  
  Purchase #2 $153.96   9.228%   $168.1674   $168.17   $168.15   $168.20  
  Purchase #3 $205.31   3.452%   $212.3973   $212.40   $212.40   $212.40  
  Purchase #4 $30.87   5.201%   $32.4755   $32.48   $32.50   $32.50  
  Purchase #5 $50.50   10.732%   $55.9197   $55.92   $55.90   $55.90  
  Purchase #6 $167.30   11.412%   $186.3923   $186.39   $186.40   $186.40  
  Purchase #7 $192.34   4.363%   $200.7318   $200.73   $200.75   $200.70  
  7 purchase totals = $1,027.81       $1,103.0951   $1,103.10   $1,103.10   $1,103.10