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 $61.68   7.253%   $66.1537   $66.15   $66.15   $66.20  
  Purchase #2 $224.79   7.166%   $240.8985   $240.90   $240.90   $240.90  
  Purchase #3 $170.53   7.844%   $183.9064   $183.91   $183.90   $183.90  
  Purchase #4 $23.49   6.739%   $25.073   $25.07   $25.05   $25.10  
  Purchase #5 $34.92   5.103%   $36.702   $36.70   $36.70   $36.70  
  Purchase #6 $11.54   12.400%   $12.971   $12.97   $12.95   $13.00  
  Purchase #7 $126.32   3.647%   $130.9269   $130.93   $130.95   $130.90  
  7 purchase totals = $653.27       $696.6315   $696.63   $696.60   $696.70