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	$169.49	12.134%	$190.0559	$190.06	$190.05	$190.10
Purchase #2	$61.61	9.544%	$67.4901	$67.49	$67.50	$67.50
Purchase #3	$69.28	6.427%	$73.7326	$73.73	$73.75	$73.70
Purchase #4	$142.88	5.745%	$151.0885	$151.09	$151.10	$151.10
Purchase #5	$240.34	3.653%	$249.1196	$249.12	$249.10	$249.10
Purchase #6	$98.54	9.784%	$108.1812	$108.18	$108.20	$108.20
Purchase #7	$233.33	11.765%	$260.7813	$260.78	$260.80	$260.80
7 purchase totals =	$1,015.47		$1,100.4492	$1,100.45	$1,100.50	$1,100.50