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	$37.74	6.172%	$40.0693	$40.07	$40.05	$40.10
Purchase #2	$239.57	12.534%	$269.5977	$269.60	$269.60	$269.60
Purchase #3	$165.37	12.165%	$185.4873	$185.49	$185.50	$185.50
Purchase #4	$69.94	3.846%	$72.6299	$72.63	$72.65	$72.60
Purchase #5	$225.56	11.521%	$251.5468	$251.55	$251.55	$251.50
Purchase #6	$88.84	4.687%	$93.0039	$93.00	$93.00	$93.00
Purchase #7	$96.43	5.321%	$101.561	$101.56	$101.55	$101.60
7 purchase totals =	$923.45		$1,013.8959	$1,013.90	$1,013.90	$1,013.90