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	$25.50	12.387%	$28.6587	$28.66	$28.65	$28.70
Purchase #2	$103.54	5.721%	$109.4635	$109.46	$109.45	$109.50
Purchase #3	$75.76	13.362%	$85.8831	$85.88	$85.90	$85.90
Purchase #4	$6.93	7.344%	$7.4389	$7.44	$7.45	$7.40
Purchase #5	$229.91	13.198%	$260.2535	$260.25	$260.25	$260.30
Purchase #6	$172.44	13.245%	$195.2797	$195.28	$195.30	$195.30
Purchase #7	$141.90	11.721%	$158.5321	$158.53	$158.55	$158.50
7 purchase totals =	$755.98		$845.5095	$845.50	$845.55	$845.60