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 $86.66   13.809%   $98.6269   $98.63   $98.65   $98.60  
  Purchase #2 $229.72   7.355%   $246.6159   $246.62   $246.60   $246.60  
  Purchase #3 $100.89   12.399%   $113.3994   $113.40   $113.40   $113.40  
  Purchase #4 $133.29   5.217%   $140.2437   $140.24   $140.25   $140.20  
  Purchase #5 $146.44   5.521%   $154.525   $154.53   $154.55   $154.50  
  Purchase #6 $203.85   4.832%   $213.7   $213.70   $213.70   $213.70  
  Purchase #7 $235.49   6.833%   $251.581   $251.58   $251.60   $251.60  
  7 purchase totals = $1,136.34       $1,218.6919   $1,218.70   $1,218.75   $1,218.60