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	$53.31	4.833%	$55.8865	$55.89	$55.90	$55.90
Purchase #2	$172.75	10.406%	$190.7264	$190.73	$190.75	$190.70
Purchase #3	$100.33	12.689%	$113.0609	$113.06	$113.05	$113.10
Purchase #4	$165.66	8.591%	$179.8919	$179.89	$179.90	$179.90
Purchase #5	$212.66	6.129%	$225.6939	$225.69	$225.70	$225.70
Purchase #6	$79.77	12.782%	$89.9662	$89.97	$89.95	$90.00
Purchase #7	$73.34	12.102%	$82.2156	$82.22	$82.20	$82.20
7 purchase totals =	$857.82		$937.4414	$937.45	$937.45	$937.50