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	$26.76	10.348%	$29.5291	$29.53	$29.55	$29.50
Purchase #2	$164.84	12.540%	$185.5109	$185.51	$185.50	$185.50
Purchase #3	$135.51	12.507%	$152.4582	$152.46	$152.45	$152.50
Purchase #4	$246.76	3.205%	$254.6687	$254.67	$254.65	$254.70
Purchase #5	$35.37	12.824%	$39.9058	$39.91	$39.90	$39.90
Purchase #6	$209.50	6.425%	$222.9604	$222.96	$222.95	$223.00
Purchase #7	$74.45	10.760%	$82.4608	$82.46	$82.45	$82.50
7 purchase totals =	$893.19		$967.4939	$967.50	$967.45	$967.60