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 $66.99   13.724%   $76.1837   $76.18   $76.20   $76.20  
  Purchase #2 $192.69   3.362%   $199.1682   $199.17   $199.15   $199.20  
  Purchase #3 $168.99   4.114%   $175.9422   $175.94   $175.95   $175.90  
  Purchase #4 $168.26   4.436%   $175.724   $175.72   $175.70   $175.70  
  Purchase #5 $146.62   13.730%   $166.7509   $166.75   $166.75   $166.80  
  Purchase #6 $56.84   3.539%   $58.8516   $58.85   $58.85   $58.90  
  Purchase #7 $212.47   12.799%   $239.664   $239.66   $239.65   $239.70  
  7 purchase totals = $1,012.86       $1,092.2846   $1,092.27   $1,092.25   $1,092.40