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	$46.78	13.705%	$53.1912	$53.19	$53.20	$53.20
Purchase #2	$79.93	11.471%	$89.0988	$89.10	$89.10	$89.10
Purchase #3	$64.80	9.400%	$70.8912	$70.89	$70.90	$70.90
Purchase #4	$19.69	4.669%	$20.6093	$20.61	$20.60	$20.60
Purchase #5	$11.31	4.220%	$11.7873	$11.79	$11.80	$11.80
Purchase #6	$61.81	5.560%	$65.2466	$65.25	$65.25	$65.20
Purchase #7	$83.86	9.380%	$91.7261	$91.73	$91.75	$91.70
7 purchase totals =	$368.18		$402.5505	$402.56	$402.60	$402.50