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 $207.28   12.176%   $232.5184   $232.52   $232.50   $232.50  
  Purchase #2 $238.50   9.253%   $260.5684   $260.57   $260.55   $260.60  
  Purchase #3 $8.87   7.125%   $9.502   $9.50   $9.50   $9.50  
  Purchase #4 $80.94   3.752%   $83.9769   $83.98   $84.00   $84.00  
  Purchase #5 $167.81   4.291%   $175.0107   $175.01   $175.00   $175.00  
  Purchase #6 $92.92   10.155%   $102.356   $102.36   $102.35   $102.40  
  Purchase #7 $230.37   8.579%   $250.1334   $250.13   $250.15   $250.10  
  7 purchase totals = $1,026.69       $1,114.0658   $1,114.07   $1,114.05   $1,114.10