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	$98.96	11.870%	$110.7066	$110.71	$110.70	$110.70
Purchase #2	$231.73	5.669%	$244.8668	$244.87	$244.85	$244.90
Purchase #3	$35.51	13.819%	$40.4171	$40.42	$40.40	$40.40
Purchase #4	$50.64	5.428%	$53.3887	$53.39	$53.40	$53.40
Purchase #5	$88.55	4.631%	$92.6508	$92.65	$92.65	$92.70
Purchase #6	$171.37	8.126%	$185.2955	$185.30	$185.30	$185.30
Purchase #7	$53.32	7.403%	$57.2673	$57.27	$57.25	$57.30
7 purchase totals =	$730.08		$784.5928	$784.61	$784.55	$784.70