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 $54.63   6.654%   $58.2651   $58.27   $58.25   $58.30  
  Purchase #2 $202.84   11.422%   $226.0084   $226.01   $226.00   $226.00  
  Purchase #3 $191.82   10.854%   $212.6401   $212.64   $212.65   $212.60  
  Purchase #4 $30.43   12.555%   $34.2505   $34.25   $34.25   $34.30  
  Purchase #5 $33.63   8.194%   $36.3856   $36.39   $36.40   $36.40  
  Purchase #6 $87.93   4.626%   $91.9976   $92.00   $92.00   $92.00  
  Purchase #7 $32.90   4.200%   $34.2818   $34.28   $34.30   $34.30  
  7 purchase totals = $634.18       $693.8291   $693.84   $693.85   $693.90