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 $64.86   6.206%   $68.8852   $68.89   $68.90   $68.90  
  Purchase #2 $103.95   9.257%   $113.5727   $113.57   $113.55   $113.60  
  Purchase #3 $207.86   8.554%   $225.6403   $225.64   $225.65   $225.60  
  Purchase #4 $5.87   13.280%   $6.6495   $6.65   $6.65   $6.60  
  Purchase #5 $148.33   7.528%   $159.4963   $159.50   $159.50   $159.50  
  Purchase #6 $77.75   4.222%   $81.0326   $81.03   $81.05   $81.00  
  Purchase #7 $86.91   7.405%   $93.3457   $93.35   $93.35   $93.30  
  7 purchase totals = $695.53       $748.6223   $748.63   $748.65   $748.50