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 $27.38   7.386%   $29.4023   $29.40   $29.40   $29.40  
  Purchase #2 $66.44   5.427%   $70.0457   $70.05   $70.05   $70.00  
  Purchase #3 $150.68   4.202%   $157.0116   $157.01   $157.00   $157.00  
  Purchase #4 $222.83   8.450%   $241.6591   $241.66   $241.65   $241.70  
  Purchase #5 $174.84   7.845%   $188.5562   $188.56   $188.55   $188.60  
  Purchase #6 $193.48   5.758%   $204.6206   $204.62   $204.60   $204.60  
  Purchase #7 $96.43   11.388%   $107.4114   $107.41   $107.40   $107.40  
  7 purchase totals = $932.08       $998.7069   $998.71   $998.65   $998.70