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	$78.70	3.617%	$81.5466	$81.55	$81.55	$81.50
Purchase #2	$88.28	13.568%	$100.2578	$100.26	$100.25	$100.30
Purchase #3	$212.66	7.818%	$229.2858	$229.29	$229.30	$229.30
Purchase #4	$40.86	5.343%	$43.0431	$43.04	$43.05	$43.00
Purchase #5	$140.97	6.851%	$150.6279	$150.63	$150.65	$150.60
Purchase #6	$38.66	10.350%	$42.6613	$42.66	$42.65	$42.70
Purchase #7	$171.89	10.213%	$189.4451	$189.45	$189.45	$189.40
7 purchase totals =	$772.02		$836.8676	$836.88	$836.90	$836.80