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 $234.37   3.452%   $242.4605   $242.46   $242.45   $242.50  
  Purchase #2 $221.71   5.865%   $234.7133   $234.71   $234.70   $234.70  
  Purchase #3 $163.42   3.110%   $168.5024   $168.50   $168.50   $168.50  
  Purchase #4 $56.92   4.129%   $59.2702   $59.27   $59.25   $59.30  
  Purchase #5 $153.88   8.659%   $167.2045   $167.20   $167.20   $167.20  
  Purchase #6 $212.25   3.362%   $219.3858   $219.39   $219.40   $219.40  
  Purchase #7 $72.91   5.817%   $77.1512   $77.15   $77.15   $77.20  
  7 purchase totals = $1,115.46       $1,168.6879   $1,168.68   $1,168.65   $1,168.80