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	$61.48	5.798%	$65.0446	$65.04	$65.05	$65.00
Purchase #2	$160.83	3.185%	$165.9524	$165.95	$165.95	$166.00
Purchase #3	$183.83	3.257%	$189.8173	$189.82	$189.80	$189.80
Purchase #4	$128.70	10.207%	$141.8364	$141.84	$141.85	$141.80
Purchase #5	$235.27	6.603%	$250.8049	$250.80	$250.80	$250.80
Purchase #6	$33.50	5.189%	$35.2383	$35.24	$35.25	$35.20
Purchase #7	$81.27	9.712%	$89.1629	$89.16	$89.15	$89.20
7 purchase totals =	$884.88		$937.8568	$937.85	$937.85	$937.80