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 $8.82   3.608%   $9.1382   $9.14   $9.15   $9.10  
  Purchase #2 $229.60   6.701%   $244.9855   $244.99   $245.00   $245.00  
  Purchase #3 $16.46   11.732%   $18.3911   $18.39   $18.40   $18.40  
  Purchase #4 $89.43   7.708%   $96.3233   $96.32   $96.30   $96.30  
  Purchase #5 $48.32   4.410%   $50.4509   $50.45   $50.45   $50.50  
  Purchase #6 $41.70   11.436%   $46.4688   $46.47   $46.45   $46.50  
  Purchase #7 $68.49   13.319%   $77.6122   $77.61   $77.60   $77.60  
  7 purchase totals = $502.82       $543.3700   $543.37   $543.35   $543.40