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	$170.61	5.753%	$180.4252	$180.43	$180.45	$180.40
Purchase #2	$45.61	10.273%	$50.2955	$50.30	$50.30	$50.30
Purchase #3	$110.38	11.755%	$123.3552	$123.36	$123.35	$123.40
Purchase #4	$111.96	6.423%	$119.1512	$119.15	$119.15	$119.20
Purchase #5	$208.81	4.832%	$218.8997	$218.90	$218.90	$218.90
Purchase #6	$28.90	12.125%	$32.4041	$32.40	$32.40	$32.40
Purchase #7	$57.28	13.462%	$64.991	$64.99	$65.00	$65.00
7 purchase totals =	$733.55		$789.5219	$789.53	$789.55	$789.60