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	$68.44	3.407%	$70.7718	$70.77	$70.75	$70.80
Purchase #2	$187.58	6.364%	$199.5176	$199.52	$199.50	$199.50
Purchase #3	$14.25	5.345%	$15.0117	$15.01	$15.00	$15.00
Purchase #4	$37.77	4.531%	$39.4814	$39.48	$39.50	$39.50
Purchase #5	$200.69	4.496%	$209.713	$209.71	$209.70	$209.70
Purchase #6	$80.46	11.112%	$89.4007	$89.40	$89.40	$89.40
Purchase #7	$210.65	5.420%	$222.0672	$222.07	$222.05	$222.10
7 purchase totals =	$799.84		$845.9634	$845.96	$845.90	$846.00