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 $206.61   13.729%   $234.9755   $234.98   $235.00   $235.00  
  Purchase #2 $221.29   4.175%   $230.5289   $230.53   $230.55   $230.50  
  Purchase #3 $43.67   12.179%   $48.9886   $48.99   $49.00   $49.00  
  Purchase #4 $15.35   12.473%   $17.2646   $17.26   $17.25   $17.30  
  Purchase #5 $77.83   5.618%   $82.2025   $82.20   $82.20   $82.20  
  Purchase #6 $205.81   9.317%   $224.9853   $224.99   $225.00   $225.00  
  Purchase #7 $217.37   13.145%   $245.9433   $245.94   $245.95   $245.90  
  7 purchase totals = $987.93       $1,084.8887   $1,084.89   $1,084.95   $1,084.90