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	$231.73	9.349%	$253.3944	$253.39	$253.40	$253.40
Purchase #2	$88.32	5.183%	$92.8976	$92.90	$92.90	$92.90
Purchase #3	$154.47	3.648%	$160.1051	$160.11	$160.10	$160.10
Purchase #4	$243.33	8.646%	$264.3683	$264.37	$264.35	$264.40
Purchase #5	$204.74	5.149%	$215.2821	$215.28	$215.30	$215.30
Purchase #6	$165.89	12.642%	$186.8618	$186.86	$186.85	$186.90
Purchase #7	$139.53	6.183%	$148.1571	$148.16	$148.15	$148.20
7 purchase totals =	$1,228.01		$1,321.0664	$1,321.07	$1,321.05	$1,321.20