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	$34.28	4.655%	$35.8757	$35.88	$35.90	$35.90
Purchase #2	$140.71	13.220%	$159.3119	$159.31	$159.30	$159.30
Purchase #3	$248.40	9.149%	$271.1261	$271.13	$271.15	$271.10
Purchase #4	$140.46	8.737%	$152.732	$152.73	$152.75	$152.70
Purchase #5	$55.37	11.662%	$61.8272	$61.83	$61.85	$61.80
Purchase #6	$40.35	7.755%	$43.4791	$43.48	$43.50	$43.50
Purchase #7	$124.64	12.598%	$140.3421	$140.34	$140.35	$140.30
7 purchase totals =	$784.21		$864.6941	$864.70	$864.80	$864.60