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 $245.76   9.314%   $268.6501   $268.65   $268.65   $268.70  
  Purchase #2 $186.31   7.273%   $199.8603   $199.86   $199.85   $199.90  
  Purchase #3 $60.30   8.373%   $65.3489   $65.35   $65.35   $65.30  
  Purchase #4 $222.87   8.618%   $242.0769   $242.08   $242.10   $242.10  
  Purchase #5 $171.50   10.179%   $188.957   $188.96   $188.95   $189.00  
  Purchase #6 $177.66   11.593%   $198.2561   $198.26   $198.25   $198.30  
  Purchase #7 $224.94   8.244%   $243.4841   $243.48   $243.50   $243.50  
  7 purchase totals = $1,289.34       $1,406.6334   $1,406.64   $1,406.65   $1,406.80