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	$91.72	9.260%	$100.2133	$100.21	$100.20	$100.20
Purchase #2	$170.90	10.655%	$189.1094	$189.11	$189.10	$189.10
Purchase #3	$246.55	11.578%	$275.0956	$275.10	$275.10	$275.10
Purchase #4	$201.67	10.331%	$222.5045	$222.50	$222.50	$222.50
Purchase #5	$140.31	12.627%	$158.0269	$158.03	$158.05	$158.00
Purchase #6	$190.89	10.620%	$211.1625	$211.16	$211.15	$211.20
Purchase #7	$29.48	5.463%	$31.0905	$31.09	$31.10	$31.10
7 purchase totals =	$1,071.52		$1,187.2027	$1,187.20	$1,187.20	$1,187.20