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	$99.96	3.202%	$103.1607	$103.16	$103.15	$103.20
Purchase #2	$243.31	7.770%	$262.2152	$262.22	$262.20	$262.20
Purchase #3	$22.76	13.824%	$25.9063	$25.91	$25.90	$25.90
Purchase #4	$145.56	11.400%	$162.1538	$162.15	$162.15	$162.20
Purchase #5	$105.49	3.642%	$109.3319	$109.33	$109.35	$109.30
Purchase #6	$89.31	11.383%	$99.4762	$99.48	$99.50	$99.50
Purchase #7	$35.70	9.646%	$39.1436	$39.14	$39.15	$39.10
7 purchase totals =	$742.09		$801.3877	$801.39	$801.40	$801.40