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	$152.87	11.220%	$170.022	$170.02	$170.00	$170.00
Purchase #2	$54.56	7.268%	$58.5254	$58.53	$58.55	$58.50
Purchase #3	$131.89	7.563%	$141.8648	$141.86	$141.85	$141.90
Purchase #4	$70.97	10.413%	$78.3601	$78.36	$78.35	$78.40
Purchase #5	$218.38	13.189%	$247.1821	$247.18	$247.20	$247.20
Purchase #6	$45.35	10.708%	$50.2061	$50.21	$50.20	$50.20
Purchase #7	$188.78	4.114%	$196.5464	$196.55	$196.55	$196.50
7 purchase totals =	$862.80		$942.7069	$942.71	$942.70	$942.70