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	$189.40	12.404%	$212.8932	$212.89	$212.90	$212.90
Purchase #2	$139.42	12.237%	$156.4808	$156.48	$156.50	$156.50
Purchase #3	$160.41	8.520%	$174.0769	$174.08	$174.10	$174.10
Purchase #4	$215.33	3.474%	$222.8106	$222.81	$222.80	$222.80
Purchase #5	$245.62	11.173%	$273.0631	$273.06	$273.05	$273.10
Purchase #6	$146.43	12.707%	$165.0369	$165.04	$165.05	$165.00
Purchase #7	$180.60	7.843%	$194.7645	$194.76	$194.75	$194.80
7 purchase totals =	$1,277.21		$1,399.1260	$1,399.12	$1,399.15	$1,399.20