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	$228.66	6.199%	$242.8346	$242.83	$242.85	$242.80
Purchase #2	$71.63	7.468%	$76.9793	$76.98	$77.00	$77.00
Purchase #3	$151.26	13.566%	$171.7799	$171.78	$171.80	$171.80
Purchase #4	$37.49	6.803%	$40.0404	$40.04	$40.05	$40.00
Purchase #5	$32.35	8.628%	$35.1412	$35.14	$35.15	$35.10
Purchase #6	$27.89	12.299%	$31.3202	$31.32	$31.30	$31.30
Purchase #7	$243.53	7.617%	$262.0797	$262.08	$262.10	$262.10
7 purchase totals =	$792.81		$860.1753	$860.17	$860.25	$860.10