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	$90.47	10.701%	$100.1512	$100.15	$100.15	$100.20
Purchase #2	$53.92	11.715%	$60.2367	$60.24	$60.25	$60.20
Purchase #3	$250.56	9.844%	$275.2251	$275.23	$275.25	$275.20
Purchase #4	$31.95	7.148%	$34.2338	$34.23	$34.25	$34.20
Purchase #5	$82.65	10.573%	$91.3886	$91.39	$91.40	$91.40
Purchase #6	$32.61	8.516%	$35.3871	$35.39	$35.40	$35.40
Purchase #7	$169.61	11.714%	$189.4781	$189.48	$189.50	$189.50
7 purchase totals =	$711.77		$786.1006	$786.11	$786.20	$786.10