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 $53.98   11.532%   $60.205   $60.21   $60.20   $60.20  
  Purchase #2 $17.81   7.538%   $19.1525   $19.15   $19.15   $19.20  
  Purchase #3 $71.72   3.250%   $74.0509   $74.05   $74.05   $74.10  
  Purchase #4 $127.63   3.480%   $132.0715   $132.07   $132.05   $132.10  
  Purchase #5 $36.66   8.599%   $39.8124   $39.81   $39.80   $39.80  
  Purchase #6 $140.70   5.166%   $147.9686   $147.97   $147.95   $148.00  
  Purchase #7 $206.83   9.674%   $226.8387   $226.84   $226.85   $226.80  
  7 purchase totals = $655.33       $700.0996   $700.10   $700.05   $700.20