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	$222.58	10.272%	$245.4434	$245.44	$245.45	$245.40
Purchase #2	$209.28	13.774%	$238.1062	$238.11	$238.10	$238.10
Purchase #3	$92.73	11.717%	$103.5952	$103.60	$103.60	$103.60
Purchase #4	$250.89	7.381%	$269.4082	$269.41	$269.40	$269.40
Purchase #5	$77.57	13.354%	$87.9287	$87.93	$87.95	$87.90
Purchase #6	$82.68	6.671%	$88.1956	$88.20	$88.20	$88.20
Purchase #7	$59.48	13.412%	$67.4575	$67.46	$67.45	$67.50
7 purchase totals =	$995.21		$1,100.1348	$1,100.15	$1,100.15	$1,100.10