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	$69.36	4.256%	$72.312	$72.31	$72.30	$72.30
Purchase #2	$225.89	11.132%	$251.0361	$251.04	$251.05	$251.00
Purchase #3	$96.49	10.281%	$106.4101	$106.41	$106.40	$106.40
Purchase #4	$227.30	9.231%	$248.2821	$248.28	$248.30	$248.30
Purchase #5	$247.82	4.740%	$259.5667	$259.57	$259.55	$259.60
Purchase #6	$99.63	9.829%	$109.4226	$109.42	$109.40	$109.40
Purchase #7	$203.78	9.713%	$223.5732	$223.57	$223.55	$223.60
7 purchase totals =	$1,170.27		$1,270.6028	$1,270.60	$1,270.55	$1,270.60