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	$238.73	4.856%	$250.3227	$250.32	$250.30	$250.30
Purchase #2	$49.57	3.568%	$51.3387	$51.34	$51.35	$51.30
Purchase #3	$12.27	11.194%	$13.6435	$13.64	$13.65	$13.60
Purchase #4	$140.49	11.120%	$156.1125	$156.11	$156.10	$156.10
Purchase #5	$48.39	11.340%	$53.8774	$53.88	$53.90	$53.90
Purchase #6	$102.46	7.424%	$110.0666	$110.07	$110.05	$110.10
Purchase #7	$157.78	4.254%	$164.492	$164.49	$164.50	$164.50
7 purchase totals =	$749.69		$799.8534	$799.85	$799.85	$799.80