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 $65.58   12.328%   $73.6647   $73.66   $73.65   $73.70  
  Purchase #2 $129.50   10.140%   $142.6313   $142.63   $142.65   $142.60  
  Purchase #3 $12.72   12.870%   $14.3571   $14.36   $14.35   $14.40  
  Purchase #4 $52.94   3.488%   $54.7865   $54.79   $54.80   $54.80  
  Purchase #5 $222.50   7.494%   $239.1742   $239.17   $239.15   $239.20  
  Purchase #6 $213.53   3.383%   $220.7537   $220.75   $220.75   $220.80  
  Purchase #7 $232.29   10.306%   $256.2298   $256.23   $256.25   $256.20  
  7 purchase totals = $929.06       $1,001.5973   $1,001.59   $1,001.60   $1,001.70