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	$46.89	10.388%	$51.7609	$51.76	$51.75	$51.80
Purchase #2	$137.38	10.542%	$151.8626	$151.86	$151.85	$151.90
Purchase #3	$249.65	13.242%	$282.7087	$282.71	$282.70	$282.70
Purchase #4	$121.53	9.577%	$133.1689	$133.17	$133.15	$133.20
Purchase #5	$30.91	7.760%	$33.3086	$33.31	$33.30	$33.30
Purchase #6	$250.31	3.776%	$259.7617	$259.76	$259.75	$259.80
Purchase #7	$196.58	7.344%	$211.0168	$211.02	$211.00	$211.00
7 purchase totals =	$1,033.25		$1,123.5882	$1,123.59	$1,123.50	$1,123.70