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	$165.81	12.311%	$186.2229	$186.22	$186.20	$186.20
Purchase #2	$219.61	11.793%	$245.5086	$245.51	$245.50	$245.50
Purchase #3	$81.58	9.762%	$89.5438	$89.54	$89.55	$89.50
Purchase #4	$126.29	13.496%	$143.3341	$143.33	$143.35	$143.30
Purchase #5	$84.84	7.412%	$91.1283	$91.13	$91.15	$91.10
Purchase #6	$18.63	11.511%	$20.7745	$20.77	$20.75	$20.80
Purchase #7	$98.89	10.633%	$109.405	$109.41	$109.40	$109.40
7 purchase totals =	$795.65		$885.9172	$885.91	$885.90	$885.80