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	$135.25	9.756%	$148.445	$148.45	$148.45	$148.40
Purchase #2	$225.77	9.725%	$247.7261	$247.73	$247.75	$247.70
Purchase #3	$96.96	3.186%	$100.0491	$100.05	$100.05	$100.00
Purchase #4	$90.62	6.428%	$96.4451	$96.45	$96.45	$96.40
Purchase #5	$169.89	11.616%	$189.6244	$189.62	$189.60	$189.60
Purchase #6	$98.65	13.648%	$112.1138	$112.11	$112.10	$112.10
Purchase #7	$79.33	5.231%	$83.4798	$83.48	$83.50	$83.50
7 purchase totals =	$896.47		$977.8833	$977.89	$977.90	$977.70