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	$18.54	3.339%	$19.1591	$19.16	$19.15	$19.20
Purchase #2	$240.90	12.369%	$270.6969	$270.70	$270.70	$270.70
Purchase #3	$50.65	5.479%	$53.4251	$53.43	$53.45	$53.40
Purchase #4	$16.96	10.715%	$18.7773	$18.78	$18.80	$18.80
Purchase #5	$25.62	5.592%	$27.0527	$27.05	$27.05	$27.10
Purchase #6	$234.87	4.376%	$245.1479	$245.15	$245.15	$245.10
Purchase #7	$56.43	5.460%	$59.5111	$59.51	$59.50	$59.50
7 purchase totals =	$643.97		$693.7701	$693.78	$693.80	$693.80