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 $66.76   8.782%   $72.6229   $72.62   $72.60   $72.60  
  Purchase #2 $43.91   6.601%   $46.8085   $46.81   $46.80   $46.80  
  Purchase #3 $88.98   8.209%   $96.2844   $96.28   $96.30   $96.30  
  Purchase #4 $144.76   10.676%   $160.2146   $160.21   $160.20   $160.20  
  Purchase #5 $41.37   9.820%   $45.4325   $45.43   $45.45   $45.40  
  Purchase #6 $20.60   10.128%   $22.6864   $22.69   $22.70   $22.70  
  Purchase #7 $17.35   3.517%   $17.9602   $17.96   $17.95   $18.00  
  7 purchase totals = $423.73       $462.0095   $462.00   $462.00   $462.00