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 $44.46   11.723%   $49.672   $49.67   $49.65   $49.70  
  Purchase #2 $73.70   13.533%   $83.6738   $83.67   $83.65   $83.70  
  Purchase #3 $66.66   13.680%   $75.7791   $75.78   $75.80   $75.80  
  Purchase #4 $83.34   4.781%   $87.3245   $87.32   $87.30   $87.30  
  Purchase #5 $170.72   8.713%   $185.5948   $185.59   $185.60   $185.60  
  Purchase #6 $219.55   9.712%   $240.8727   $240.87   $240.85   $240.90  
  Purchase #7 $166.30   5.681%   $175.7475   $175.75   $175.75   $175.70  
  7 purchase totals = $824.73       $898.6644   $898.65   $898.60   $898.70