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	$59.80	5.202%	$62.9108	$62.91	$62.90	$62.90
Purchase #2	$15.90	8.511%	$17.2532	$17.25	$17.25	$17.30
Purchase #3	$79.27	12.731%	$89.3619	$89.36	$89.35	$89.40
Purchase #4	$40.62	4.369%	$42.3947	$42.39	$42.40	$42.40
Purchase #5	$77.48	4.544%	$81.0007	$81.00	$81.00	$81.00
Purchase #6	$107.48	13.331%	$121.8082	$121.81	$121.80	$121.80
Purchase #7	$145.27	10.615%	$160.6904	$160.69	$160.70	$160.70
7 purchase totals =	$525.82		$575.4199	$575.41	$575.40	$575.50