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	$30.64	6.214%	$32.544	$32.54	$32.55	$32.50
Purchase #2	$185.30	8.386%	$200.8393	$200.84	$200.85	$200.80
Purchase #3	$122.57	10.598%	$135.56	$135.56	$135.55	$135.60
Purchase #4	$9.92	6.770%	$10.5916	$10.59	$10.60	$10.60
Purchase #5	$220.77	4.789%	$231.3427	$231.34	$231.35	$231.30
Purchase #6	$247.37	8.386%	$268.1144	$268.11	$268.10	$268.10
Purchase #7	$56.35	5.240%	$59.3027	$59.30	$59.30	$59.30
7 purchase totals =	$872.92		$938.2947	$938.28	$938.30	$938.20