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 $222.81   8.575%   $241.916   $241.92   $241.90   $241.90  
  Purchase #2 $77.27   7.781%   $83.2824   $83.28   $83.30   $83.30  
  Purchase #3 $175.34   9.305%   $191.6554   $191.66   $191.65   $191.70  
  Purchase #4 $238.71   7.315%   $256.1716   $256.17   $256.15   $256.20  
  Purchase #5 $10.92   12.435%   $12.2779   $12.28   $12.30   $12.30  
  Purchase #6 $126.60   9.115%   $138.1396   $138.14   $138.15   $138.10  
  Purchase #7 $21.72   10.402%   $23.9793   $23.98   $24.00   $24.00  
  7 purchase totals = $873.37       $947.4222   $947.43   $947.45   $947.50