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	$223.84	6.370%	$238.0986	$238.10	$238.10	$238.10
Purchase #2	$152.41	13.265%	$172.6272	$172.63	$172.65	$172.60
Purchase #3	$235.84	4.118%	$245.5519	$245.55	$245.55	$245.60
Purchase #4	$78.70	8.141%	$85.107	$85.11	$85.10	$85.10
Purchase #5	$128.79	11.765%	$143.9421	$143.94	$143.95	$143.90
Purchase #6	$34.61	7.445%	$37.1867	$37.19	$37.20	$37.20
Purchase #7	$31.79	4.684%	$33.279	$33.28	$33.30	$33.30
7 purchase totals =	$885.98		$955.7925	$955.80	$955.85	$955.80