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	$26.35	9.589%	$28.8767	$28.88	$28.90	$28.90
Purchase #2	$32.70	13.277%	$37.0416	$37.04	$37.05	$37.00
Purchase #3	$218.42	6.797%	$233.266	$233.27	$233.25	$233.30
Purchase #4	$50.59	6.227%	$53.7402	$53.74	$53.75	$53.70
Purchase #5	$182.71	3.324%	$188.7833	$188.78	$188.80	$188.80
Purchase #6	$67.43	7.236%	$72.3092	$72.31	$72.30	$72.30
Purchase #7	$94.68	3.559%	$98.0497	$98.05	$98.05	$98.00
7 purchase totals =	$672.88		$712.0667	$712.07	$712.10	$712.00