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	$90.70	9.287%	$99.1233	$99.12	$99.10	$99.10
Purchase #2	$16.44	12.670%	$18.5229	$18.52	$18.50	$18.50
Purchase #3	$209.60	6.155%	$222.5009	$222.50	$222.50	$222.50
Purchase #4	$143.45	4.122%	$149.363	$149.36	$149.35	$149.40
Purchase #5	$66.37	11.366%	$73.9136	$73.91	$73.90	$73.90
Purchase #6	$131.52	13.710%	$149.5514	$149.55	$149.55	$149.60
Purchase #7	$195.59	12.411%	$219.8647	$219.86	$219.85	$219.90
7 purchase totals =	$853.67		$932.8398	$932.82	$932.75	$932.90