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	$78.86	3.537%	$81.6493	$81.65	$81.65	$81.60
Purchase #2	$56.68	7.330%	$60.8346	$60.83	$60.85	$60.80
Purchase #3	$71.47	3.304%	$73.8314	$73.83	$73.85	$73.80
Purchase #4	$43.42	4.831%	$45.5176	$45.52	$45.50	$45.50
Purchase #5	$179.68	6.767%	$191.8389	$191.84	$191.85	$191.80
Purchase #6	$245.59	7.751%	$264.6257	$264.63	$264.65	$264.60
Purchase #7	$122.80	6.453%	$130.7243	$130.72	$130.70	$130.70
7 purchase totals =	$798.50		$849.0218	$849.02	$849.05	$848.80