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	$243.77	13.144%	$275.8111	$275.81	$275.80	$275.80
Purchase #2	$152.87	7.475%	$164.297	$164.30	$164.30	$164.30
Purchase #3	$50.88	12.144%	$57.0589	$57.06	$57.05	$57.10
Purchase #4	$224.91	6.674%	$239.9205	$239.92	$239.90	$239.90
Purchase #5	$196.96	3.235%	$203.3317	$203.33	$203.35	$203.30
Purchase #6	$238.39	7.244%	$255.659	$255.66	$255.65	$255.70
Purchase #7	$72.83	6.424%	$77.5086	$77.51	$77.50	$77.50
7 purchase totals =	$1,180.61		$1,273.5868	$1,273.59	$1,273.55	$1,273.60