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	$188.77	10.755%	$209.0722	$209.07	$209.05	$209.10
Purchase #2	$128.56	13.341%	$145.7112	$145.71	$145.70	$145.70
Purchase #3	$243.90	12.731%	$274.9509	$274.95	$274.95	$275.00
Purchase #4	$131.69	10.340%	$145.3067	$145.31	$145.30	$145.30
Purchase #5	$168.62	13.832%	$191.9435	$191.94	$191.95	$191.90
Purchase #6	$32.68	3.616%	$33.8617	$33.86	$33.85	$33.90
Purchase #7	$171.50	9.542%	$187.8645	$187.86	$187.85	$187.90
7 purchase totals =	$1,065.72		$1,188.7107	$1,188.70	$1,188.65	$1,188.80