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	$205.62	10.482%	$227.1731	$227.17	$227.15	$227.20
Purchase #2	$23.96	3.424%	$24.7804	$24.78	$24.80	$24.80
Purchase #3	$87.62	13.261%	$99.2393	$99.24	$99.25	$99.20
Purchase #4	$10.49	3.816%	$10.8903	$10.89	$10.90	$10.90
Purchase #5	$115.71	13.840%	$131.7243	$131.72	$131.70	$131.70
Purchase #6	$207.55	10.605%	$229.5607	$229.56	$229.55	$229.60
Purchase #7	$69.47	9.223%	$75.8772	$75.88	$75.90	$75.90
7 purchase totals =	$720.42		$799.2453	$799.24	$799.25	$799.30