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	$84.47	7.148%	$90.5079	$90.51	$90.50	$90.50
Purchase #2	$35.29	13.582%	$40.0831	$40.08	$40.10	$40.10
Purchase #3	$31.70	6.415%	$33.7336	$33.73	$33.75	$33.70
Purchase #4	$116.27	13.343%	$131.7839	$131.78	$131.80	$131.80
Purchase #5	$19.75	13.754%	$22.4664	$22.47	$22.45	$22.50
Purchase #6	$158.93	3.860%	$165.0647	$165.06	$165.05	$165.10
Purchase #7	$6.46	10.321%	$7.1267	$7.13	$7.15	$7.10
7 purchase totals =	$452.87		$490.7663	$490.76	$490.80	$490.80