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	$33.67	10.778%	$37.299	$37.30	$37.30	$37.30
Purchase #2	$174.26	9.352%	$190.5568	$190.56	$190.55	$190.60
Purchase #3	$182.78	9.550%	$200.2355	$200.24	$200.25	$200.20
Purchase #4	$149.69	13.482%	$169.8712	$169.87	$169.85	$169.90
Purchase #5	$121.96	6.834%	$130.2947	$130.29	$130.30	$130.30
Purchase #6	$99.68	7.842%	$107.4969	$107.50	$107.50	$107.50
Purchase #7	$33.42	6.345%	$35.5405	$35.54	$35.55	$35.50
7 purchase totals =	$795.46		$871.2946	$871.30	$871.30	$871.30