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	$56.51	7.428%	$60.7076	$60.71	$60.70	$60.70
Purchase #2	$99.30	10.586%	$109.8119	$109.81	$109.80	$109.80
Purchase #3	$135.69	10.676%	$150.1763	$150.18	$150.20	$150.20
Purchase #4	$72.73	10.867%	$80.6336	$80.63	$80.65	$80.60
Purchase #5	$133.41	10.483%	$147.3954	$147.40	$147.40	$147.40
Purchase #6	$51.78	13.123%	$58.5751	$58.58	$58.60	$58.60
Purchase #7	$179.96	11.394%	$200.4646	$200.46	$200.45	$200.50
7 purchase totals =	$729.38		$807.7645	$807.77	$807.80	$807.80