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	$106.94	13.596%	$121.4796	$121.48	$121.50	$121.50
Purchase #2	$37.80	7.726%	$40.7204	$40.72	$40.70	$40.70
Purchase #3	$82.53	11.178%	$91.7552	$91.76	$91.75	$91.80
Purchase #4	$19.44	8.773%	$21.1455	$21.15	$21.15	$21.10
Purchase #5	$100.31	8.811%	$109.1483	$109.15	$109.15	$109.10
Purchase #6	$159.50	13.316%	$180.739	$180.74	$180.75	$180.70
Purchase #7	$169.40	11.510%	$188.8979	$188.90	$188.90	$188.90
7 purchase totals =	$675.92		$753.8859	$753.90	$753.90	$753.80