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 $94.36   13.673%   $107.2618   $107.26   $107.25   $107.30  
  Purchase #2 $166.34   3.269%   $171.7777   $171.78   $171.80   $171.80  
  Purchase #3 $195.62   6.140%   $207.6311   $207.63   $207.65   $207.60  
  Purchase #4 $62.62   3.158%   $64.5975   $64.60   $64.60   $64.60  
  Purchase #5 $7.66   9.227%   $8.3668   $8.37   $8.35   $8.40  
  Purchase #6 $183.52   4.744%   $192.2262   $192.23   $192.25   $192.20  
  Purchase #7 $207.44   7.404%   $222.7989   $222.80   $222.80   $222.80  
  7 purchase totals = $917.56       $974.6600   $974.67   $974.70   $974.70