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 $64.66   13.580%   $73.4408   $73.44   $73.45   $73.40  
  Purchase #2 $159.86   4.388%   $166.8747   $166.87   $166.85   $166.90  
  Purchase #3 $8.51   7.543%   $9.1519   $9.15   $9.15   $9.20  
  Purchase #4 $215.75   6.277%   $229.2926   $229.29   $229.30   $229.30  
  Purchase #5 $134.99   7.719%   $145.4099   $145.41   $145.40   $145.40  
  Purchase #6 $83.92   3.845%   $87.1467   $87.15   $87.15   $87.10  
  Purchase #7 $224.94   6.162%   $238.8008   $238.80   $238.80   $238.80  
  7 purchase totals = $892.63       $950.1174   $950.11   $950.10   $950.10