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	$221.64	6.560%	$236.1796	$236.18	$236.20	$236.20
Purchase #2	$154.69	11.516%	$172.5041	$172.50	$172.50	$172.50
Purchase #3	$17.38	6.758%	$18.5545	$18.55	$18.55	$18.60
Purchase #4	$7.26	12.396%	$8.1599	$8.16	$8.15	$8.20
Purchase #5	$161.72	6.202%	$171.7499	$171.75	$171.75	$171.70
Purchase #6	$105.79	3.778%	$109.7867	$109.79	$109.80	$109.80
Purchase #7	$80.35	11.212%	$89.3588	$89.36	$89.35	$89.40
7 purchase totals =	$748.83		$806.2935	$806.29	$806.30	$806.40