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	$136.75	9.294%	$149.4595	$149.46	$149.45	$149.50
Purchase #2	$78.48	12.825%	$88.5451	$88.55	$88.55	$88.50
Purchase #3	$210.29	11.227%	$233.8993	$233.90	$233.90	$233.90
Purchase #4	$219.68	9.480%	$240.5057	$240.51	$240.50	$240.50
Purchase #5	$118.81	7.237%	$127.4083	$127.41	$127.40	$127.40
Purchase #6	$31.57	8.134%	$34.1379	$34.14	$34.15	$34.10
Purchase #7	$123.91	13.861%	$141.0852	$141.09	$141.10	$141.10
7 purchase totals =	$919.49		$1,015.0410	$1,015.06	$1,015.05	$1,015.00