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	$32.62	8.585%	$35.4204	$35.42	$35.40	$35.40
Purchase #2	$152.39	8.319%	$165.0673	$165.07	$165.05	$165.10
Purchase #3	$142.79	3.111%	$147.2322	$147.23	$147.25	$147.20
Purchase #4	$84.85	5.605%	$89.6058	$89.61	$89.60	$89.60
Purchase #5	$227.80	6.314%	$242.1833	$242.18	$242.20	$242.20
Purchase #6	$244.33	8.409%	$264.8757	$264.88	$264.90	$264.90
Purchase #7	$171.31	13.730%	$194.8309	$194.83	$194.85	$194.80
7 purchase totals =	$1,056.09		$1,139.2156	$1,139.22	$1,139.25	$1,139.20