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	$131.26	11.831%	$146.7894	$146.79	$146.80	$146.80
Purchase #2	$19.90	7.166%	$21.326	$21.33	$21.35	$21.30
Purchase #3	$37.48	7.167%	$40.1662	$40.17	$40.15	$40.20
Purchase #4	$220.57	11.167%	$245.2011	$245.20	$245.20	$245.20
Purchase #5	$69.40	8.160%	$75.063	$75.06	$75.05	$75.10
Purchase #6	$76.31	3.407%	$78.9099	$78.91	$78.90	$78.90
Purchase #7	$218.59	10.734%	$242.0535	$242.05	$242.05	$242.10
7 purchase totals =	$773.51		$849.5091	$849.51	$849.50	$849.60