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 $149.49   8.129%   $161.642   $161.64   $161.65   $161.60  
  Purchase #2 $61.42   13.871%   $69.9396   $69.94   $69.95   $69.90  
  Purchase #3 $201.46   13.614%   $228.8868   $228.89   $228.90   $228.90  
  Purchase #4 $88.76   3.458%   $91.8293   $91.83   $91.85   $91.80  
  Purchase #5 $179.54   8.513%   $194.8242   $194.82   $194.80   $194.80  
  Purchase #6 $227.92   3.357%   $235.5713   $235.57   $235.55   $235.60  
  Purchase #7 $242.30   12.105%   $271.6304   $271.63   $271.65   $271.60  
  7 purchase totals = $1,150.89       $1,254.3236   $1,254.32   $1,254.35   $1,254.20