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	$37.89	6.354%	$40.2975	$40.30	$40.30	$40.30
Purchase #2	$213.47	10.163%	$235.165	$235.17	$235.15	$235.20
Purchase #3	$226.37	7.846%	$244.131	$244.13	$244.15	$244.10
Purchase #4	$200.69	9.346%	$219.4465	$219.45	$219.45	$219.40
Purchase #5	$145.86	4.787%	$152.8423	$152.84	$152.85	$152.80
Purchase #6	$94.86	3.508%	$98.1877	$98.19	$98.20	$98.20
Purchase #7	$94.48	5.105%	$99.3032	$99.30	$99.30	$99.30
7 purchase totals =	$1,013.62		$1,089.3732	$1,089.38	$1,089.40	$1,089.30