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 $117.83   5.849%   $124.7219   $124.72   $124.70   $124.70  
  Purchase #2 $222.36   10.869%   $246.5283   $246.53   $246.55   $246.50  
  Purchase #3 $63.92   13.543%   $72.5767   $72.58   $72.60   $72.60  
  Purchase #4 $117.57   5.581%   $124.1316   $124.13   $124.15   $124.10  
  Purchase #5 $72.71   4.367%   $75.8852   $75.89   $75.90   $75.90  
  Purchase #6 $79.66   4.702%   $83.4056   $83.41   $83.40   $83.40  
  Purchase #7 $209.99   6.578%   $223.8031   $223.80   $223.80   $223.80  
  7 purchase totals = $884.04       $951.0524   $951.06   $951.10   $951.00