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 $208.65   12.502%   $234.7354   $234.74   $234.75   $234.70  
  Purchase #2 $53.88   11.239%   $59.9356   $59.94   $59.95   $59.90  
  Purchase #3 $119.77   8.312%   $129.7253   $129.73   $129.75   $129.70  
  Purchase #4 $50.72   12.113%   $56.8637   $56.86   $56.85   $56.90  
  Purchase #5 $109.95   10.218%   $121.1847   $121.18   $121.20   $121.20  
  Purchase #6 $150.44   10.501%   $166.2377   $166.24   $166.25   $166.20  
  Purchase #7 $191.70   5.516%   $202.2742   $202.27   $202.25   $202.30  
  7 purchase totals = $885.11       $970.9566   $970.96   $971.00   $970.90