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	$79.60	3.736%	$82.5739	$82.57	$82.55	$82.60
Purchase #2	$65.55	10.797%	$72.6274	$72.63	$72.65	$72.60
Purchase #3	$72.61	8.451%	$78.7463	$78.75	$78.75	$78.70
Purchase #4	$77.80	9.301%	$85.0362	$85.04	$85.05	$85.00
Purchase #5	$154.66	7.283%	$165.9239	$165.92	$165.90	$165.90
Purchase #6	$143.81	5.166%	$151.2392	$151.24	$151.25	$151.20
Purchase #7	$166.48	13.650%	$189.2045	$189.20	$189.20	$189.20
7 purchase totals =	$760.51		$825.3514	$825.35	$825.35	$825.20