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	$146.34	4.210%	$152.5009	$152.50	$152.50	$152.50
Purchase #2	$35.61	13.566%	$40.4409	$40.44	$40.45	$40.40
Purchase #3	$191.94	8.260%	$207.7942	$207.79	$207.80	$207.80
Purchase #4	$234.64	10.498%	$259.2725	$259.27	$259.25	$259.30
Purchase #5	$167.74	13.596%	$190.5459	$190.55	$190.55	$190.50
Purchase #6	$185.95	10.460%	$205.4004	$205.40	$205.40	$205.40
Purchase #7	$195.57	12.433%	$219.8852	$219.89	$219.90	$219.90
7 purchase totals =	$1,157.79		$1,275.8400	$1,275.84	$1,275.85	$1,275.80