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	$37.55	11.767%	$41.9685	$41.97	$41.95	$42.00
Purchase #2	$33.41	6.161%	$35.4684	$35.47	$35.45	$35.50
Purchase #3	$120.54	5.833%	$127.5711	$127.57	$127.55	$127.60
Purchase #4	$204.67	9.205%	$223.5099	$223.51	$223.50	$223.50
Purchase #5	$235.67	9.230%	$257.4223	$257.42	$257.40	$257.40
Purchase #6	$243.80	10.777%	$270.0743	$270.07	$270.05	$270.10
Purchase #7	$85.87	9.329%	$93.8808	$93.88	$93.90	$93.90
7 purchase totals =	$961.51		$1,049.8953	$1,049.89	$1,049.80	$1,050.00