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 $25.36   9.855%   $27.8592   $27.86   $27.85   $27.90  
  Purchase #2 $101.64   7.318%   $109.078   $109.08   $109.10   $109.10  
  Purchase #3 $204.82   13.269%   $231.9976   $232.00   $232.00   $232.00  
  Purchase #4 $203.75   10.367%   $224.8728   $224.87   $224.85   $224.90  
  Purchase #5 $66.35   3.444%   $68.6351   $68.64   $68.65   $68.60  
  Purchase #6 $208.40   8.268%   $225.6305   $225.63   $225.65   $225.60  
  Purchase #7 $185.44   3.733%   $192.3625   $192.36   $192.35   $192.40  
  7 purchase totals = $995.76       $1,080.4357   $1,080.44   $1,080.45   $1,080.50