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	$128.89	7.724%	$138.8455	$138.85	$138.85	$138.80
Purchase #2	$164.34	6.776%	$175.4757	$175.48	$175.50	$175.50
Purchase #3	$32.26	11.109%	$35.8438	$35.84	$35.85	$35.80
Purchase #4	$31.31	6.507%	$33.3473	$33.35	$33.35	$33.30
Purchase #5	$208.69	9.468%	$228.4488	$228.45	$228.45	$228.40
Purchase #6	$18.80	13.198%	$21.2812	$21.28	$21.30	$21.30
Purchase #7	$73.38	12.818%	$82.7858	$82.79	$82.80	$82.80
7 purchase totals =	$657.67		$716.0281	$716.04	$716.10	$715.90