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	$84.87	7.111%	$90.9051	$90.91	$90.90	$90.90
Purchase #2	$154.27	9.862%	$169.4841	$169.48	$169.50	$169.50
Purchase #3	$131.98	5.527%	$139.2745	$139.27	$139.25	$139.30
Purchase #4	$64.89	9.701%	$71.185	$71.19	$71.20	$71.20
Purchase #5	$80.97	9.644%	$88.7787	$88.78	$88.80	$88.80
Purchase #6	$247.88	12.103%	$277.8809	$277.88	$277.90	$277.90
Purchase #7	$165.75	10.204%	$182.6631	$182.66	$182.65	$182.70
7 purchase totals =	$930.61		$1,020.1714	$1,020.17	$1,020.20	$1,020.30