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	$170.90	11.134%	$189.928	$189.93	$189.95	$189.90
Purchase #2	$96.50	10.329%	$106.4675	$106.47	$106.45	$106.50
Purchase #3	$36.48	7.751%	$39.3076	$39.31	$39.30	$39.30
Purchase #4	$210.61	3.759%	$218.5268	$218.53	$218.55	$218.50
Purchase #5	$191.83	4.314%	$200.1055	$200.11	$200.10	$200.10
Purchase #6	$61.79	7.795%	$66.6065	$66.61	$66.60	$66.60
Purchase #7	$213.31	8.381%	$231.1875	$231.19	$231.20	$231.20
7 purchase totals =	$981.42		$1,052.1294	$1,052.15	$1,052.15	$1,052.10