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 $22.81   12.325%   $25.6213   $25.62   $25.60   $25.60  
  Purchase #2 $209.36   9.415%   $229.0712   $229.07   $229.05   $229.10  
  Purchase #3 $217.68   9.358%   $238.0505   $238.05   $238.05   $238.10  
  Purchase #4 $46.27   7.647%   $49.8083   $49.81   $49.80   $49.80  
  Purchase #5 $143.51   6.122%   $152.2957   $152.30   $152.30   $152.30  
  Purchase #6 $136.80   11.578%   $152.6387   $152.64   $152.65   $152.60  
  Purchase #7 $135.82   9.329%   $148.4906   $148.49   $148.50   $148.50  
  7 purchase totals = $912.25       $995.9763   $995.98   $995.95   $996.00