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	$102.36	8.567%	$111.1292	$111.13	$111.15	$111.10
Purchase #2	$28.27	4.454%	$29.5291	$29.53	$29.55	$29.50
Purchase #3	$147.50	8.314%	$159.7632	$159.76	$159.75	$159.80
Purchase #4	$139.88	4.506%	$146.183	$146.18	$146.20	$146.20
Purchase #5	$29.90	11.571%	$33.3597	$33.36	$33.35	$33.40
Purchase #6	$217.50	13.822%	$247.5629	$247.56	$247.55	$247.60
Purchase #7	$58.56	10.642%	$64.792	$64.79	$64.80	$64.80
7 purchase totals =	$723.97		$792.3191	$792.31	$792.35	$792.40