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	$205.33	10.777%	$227.4584	$227.46	$227.45	$227.50
Purchase #2	$174.73	4.315%	$182.2696	$182.27	$182.25	$182.30
Purchase #3	$54.44	11.133%	$60.5008	$60.50	$60.50	$60.50
Purchase #4	$140.33	3.766%	$145.6148	$145.61	$145.60	$145.60
Purchase #5	$185.88	9.870%	$204.2264	$204.23	$204.25	$204.20
Purchase #6	$13.59	4.234%	$14.1654	$14.17	$14.15	$14.20
Purchase #7	$130.48	6.743%	$139.2783	$139.28	$139.30	$139.30
7 purchase totals =	$904.78		$973.5137	$973.52	$973.50	$973.60