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 $57.54   6.122%   $61.0626   $61.06   $61.05   $61.10  
  Purchase #2 $119.58   12.515%   $134.5454   $134.55   $134.55   $134.50  
  Purchase #3 $167.70   7.439%   $180.1752   $180.18   $180.20   $180.20  
  Purchase #4 $106.85   9.331%   $116.8202   $116.82   $116.80   $116.80  
  Purchase #5 $118.88   5.188%   $125.0475   $125.05   $125.05   $125.00  
  Purchase #6 $45.76   8.566%   $49.6798   $49.68   $49.70   $49.70  
  Purchase #7 $240.88   11.554%   $268.7113   $268.71   $268.70   $268.70  
  7 purchase totals = $857.19       $936.0420   $936.05   $936.05   $936.00