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	$218.54	12.293%	$245.4051	$245.41	$245.40	$245.40
Purchase #2	$234.95	9.765%	$257.8929	$257.89	$257.90	$257.90
Purchase #3	$89.64	9.496%	$98.1522	$98.15	$98.15	$98.20
Purchase #4	$170.31	8.714%	$185.1508	$185.15	$185.15	$185.20
Purchase #5	$89.61	11.242%	$99.684	$99.68	$99.70	$99.70
Purchase #6	$111.45	7.515%	$119.8255	$119.83	$119.85	$119.80
Purchase #7	$168.41	8.695%	$183.0532	$183.05	$183.05	$183.10
7 purchase totals =	$1,082.91		$1,189.1637	$1,189.16	$1,189.20	$1,189.30