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	$155.55	6.611%	$165.8334	$165.83	$165.85	$165.80
Purchase #2	$109.96	12.614%	$123.8304	$123.83	$123.85	$123.80
Purchase #3	$39.55	3.770%	$41.041	$41.04	$41.05	$41.00
Purchase #4	$247.79	10.376%	$273.5007	$273.50	$273.50	$273.50
Purchase #5	$77.57	7.397%	$83.3079	$83.31	$83.30	$83.30
Purchase #6	$146.55	8.743%	$159.3629	$159.36	$159.35	$159.40
Purchase #7	$15.83	13.571%	$17.9783	$17.98	$18.00	$18.00
7 purchase totals =	$792.80		$864.8546	$864.85	$864.90	$864.80