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	$40.54	11.542%	$45.2191	$45.22	$45.20	$45.20
Purchase #2	$236.48	11.804%	$264.3941	$264.39	$264.40	$264.40
Purchase #3	$56.46	12.400%	$63.461	$63.46	$63.45	$63.50
Purchase #4	$84.51	5.211%	$88.9138	$88.91	$88.90	$88.90
Purchase #5	$204.44	12.678%	$230.3589	$230.36	$230.35	$230.40
Purchase #6	$157.46	7.569%	$169.3781	$169.38	$169.40	$169.40
Purchase #7	$148.38	5.541%	$156.6017	$156.60	$156.60	$156.60
7 purchase totals =	$928.27		$1,018.3267	$1,018.32	$1,018.30	$1,018.40