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	$248.31	10.288%	$273.8561	$273.86	$273.85	$273.90
Purchase #2	$189.44	13.646%	$215.291	$215.29	$215.30	$215.30
Purchase #3	$189.44	10.790%	$209.8806	$209.88	$209.90	$209.90
Purchase #4	$151.45	6.220%	$160.8702	$160.87	$160.85	$160.90
Purchase #5	$103.59	3.204%	$106.909	$106.91	$106.90	$106.90
Purchase #6	$43.37	9.610%	$47.5379	$47.54	$47.55	$47.50
Purchase #7	$36.91	4.426%	$38.5436	$38.54	$38.55	$38.50
7 purchase totals =	$962.51		$1,052.8884	$1,052.89	$1,052.90	$1,052.90