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	$37.71	13.114%	$42.6553	$42.66	$42.65	$42.70
Purchase #2	$160.40	7.489%	$172.4124	$172.41	$172.40	$172.40
Purchase #3	$140.41	7.262%	$150.6066	$150.61	$150.60	$150.60
Purchase #4	$174.63	9.122%	$190.5597	$190.56	$190.55	$190.60
Purchase #5	$154.49	6.187%	$164.0483	$164.05	$164.05	$164.00
Purchase #6	$98.66	6.166%	$104.7434	$104.74	$104.75	$104.70
Purchase #7	$166.57	6.620%	$177.5969	$177.60	$177.60	$177.60
7 purchase totals =	$932.87		$1,002.6226	$1,002.63	$1,002.60	$1,002.60