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	$28.72	6.147%	$30.4854	$30.49	$30.50	$30.50
Purchase #2	$39.62	7.682%	$42.6636	$42.66	$42.65	$42.70
Purchase #3	$139.75	5.574%	$147.5397	$147.54	$147.55	$147.50
Purchase #4	$187.27	11.851%	$209.4634	$209.46	$209.45	$209.50
Purchase #5	$230.55	13.415%	$261.4783	$261.48	$261.50	$261.50
Purchase #6	$9.93	5.574%	$10.4835	$10.48	$10.50	$10.50
Purchase #7	$162.57	6.143%	$172.5567	$172.56	$172.55	$172.60
7 purchase totals =	$798.41		$874.6706	$874.67	$874.70	$874.80