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 $228.71   10.621%   $253.0013   $253.00   $253.00   $253.00  
  Purchase #2 $192.67   8.608%   $209.255   $209.26   $209.25   $209.30  
  Purchase #3 $144.30   8.331%   $156.3216   $156.32   $156.30   $156.30  
  Purchase #4 $18.71   10.813%   $20.7331   $20.73   $20.75   $20.70  
  Purchase #5 $20.88   13.338%   $23.665   $23.67   $23.65   $23.70  
  Purchase #6 $205.40   3.395%   $212.3733   $212.37   $212.35   $212.40  
  Purchase #7 $219.36   5.271%   $230.9225   $230.92   $230.90   $230.90  
  7 purchase totals = $1,030.03       $1,106.2718   $1,106.27   $1,106.20   $1,106.30