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	$93.50	3.220%	$96.5107	$96.51	$96.50	$96.50
Purchase #2	$147.77	7.478%	$158.8202	$158.82	$158.80	$158.80
Purchase #3	$72.50	8.508%	$78.6683	$78.67	$78.65	$78.70
Purchase #4	$88.61	11.401%	$98.7124	$98.71	$98.70	$98.70
Purchase #5	$50.99	6.512%	$54.3105	$54.31	$54.30	$54.30
Purchase #6	$131.73	7.237%	$141.2633	$141.26	$141.25	$141.30
Purchase #7	$215.55	13.503%	$244.6557	$244.66	$244.65	$244.70
7 purchase totals =	$800.65		$872.9411	$872.94	$872.85	$873.00