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	$53.54	3.590%	$55.4621	$55.46	$55.45	$55.50
Purchase #2	$37.66	8.246%	$40.7654	$40.77	$40.75	$40.80
Purchase #3	$119.76	5.146%	$125.9228	$125.92	$125.90	$125.90
Purchase #4	$152.89	6.524%	$162.8645	$162.86	$162.85	$162.90
Purchase #5	$155.45	7.537%	$167.1663	$167.17	$167.15	$167.20
Purchase #6	$221.30	5.619%	$233.7348	$233.73	$233.75	$233.70
Purchase #7	$107.61	11.808%	$120.3166	$120.32	$120.30	$120.30
7 purchase totals =	$848.21		$906.2325	$906.23	$906.15	$906.30