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 $61.49   5.283%   $64.7385   $64.74   $64.75   $64.70  
  Purchase #2 $169.94   9.388%   $185.894   $185.89   $185.90   $185.90  
  Purchase #3 $44.57   4.393%   $46.528   $46.53   $46.55   $46.50  
  Purchase #4 $211.91   5.169%   $222.8636   $222.86   $222.85   $222.90  
  Purchase #5 $112.32   8.274%   $121.6134   $121.61   $121.60   $121.60  
  Purchase #6 $196.68   5.265%   $207.0352   $207.04   $207.05   $207.00  
  Purchase #7 $89.40   5.201%   $94.0497   $94.05   $94.05   $94.00  
  7 purchase totals = $886.31       $942.7224   $942.72   $942.75   $942.60