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	$174.61	12.564%	$196.548	$196.55	$196.55	$196.50
Purchase #2	$133.96	12.121%	$150.1973	$150.20	$150.20	$150.20
Purchase #3	$126.40	4.113%	$131.5988	$131.60	$131.60	$131.60
Purchase #4	$185.78	12.533%	$209.0638	$209.06	$209.05	$209.10
Purchase #5	$80.62	6.814%	$86.1134	$86.11	$86.10	$86.10
Purchase #6	$26.62	7.346%	$28.5755	$28.58	$28.60	$28.60
Purchase #7	$106.77	3.756%	$110.7803	$110.78	$110.80	$110.80
7 purchase totals =	$834.76		$912.8771	$912.88	$912.90	$912.90