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	$54.54	9.207%	$59.5615	$59.56	$59.55	$59.60
Purchase #2	$135.57	4.373%	$141.4985	$141.50	$141.50	$141.50
Purchase #3	$248.58	6.252%	$264.1212	$264.12	$264.10	$264.10
Purchase #4	$131.47	13.443%	$149.1435	$149.14	$149.15	$149.10
Purchase #5	$68.40	4.369%	$71.3884	$71.39	$71.40	$71.40
Purchase #6	$71.79	11.501%	$80.0466	$80.05	$80.05	$80.00
Purchase #7	$232.67	9.835%	$255.5531	$255.55	$255.55	$255.60
7 purchase totals =	$943.02		$1,021.3128	$1,021.31	$1,021.30	$1,021.30