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	$179.70	5.668%	$189.8854	$189.89	$189.90	$189.90
Purchase #2	$18.99	6.111%	$20.1505	$20.15	$20.15	$20.20
Purchase #3	$212.52	5.375%	$223.943	$223.94	$223.95	$223.90
Purchase #4	$243.33	5.352%	$256.353	$256.35	$256.35	$256.40
Purchase #5	$69.96	12.795%	$78.9114	$78.91	$78.90	$78.90
Purchase #6	$34.81	8.277%	$37.6912	$37.69	$37.70	$37.70
Purchase #7	$73.96	8.477%	$80.2296	$80.23	$80.25	$80.20
7 purchase totals =	$833.27		$887.1641	$887.16	$887.20	$887.20