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	$45.76	13.290%	$51.8415	$51.84	$51.85	$51.80
Purchase #2	$160.38	9.187%	$175.1141	$175.11	$175.10	$175.10
Purchase #3	$168.96	6.669%	$180.2279	$180.23	$180.25	$180.20
Purchase #4	$73.45	13.443%	$83.3239	$83.32	$83.30	$83.30
Purchase #5	$183.47	9.191%	$200.3327	$200.33	$200.35	$200.30
Purchase #6	$238.26	3.809%	$247.3353	$247.34	$247.35	$247.30
Purchase #7	$212.77	13.659%	$241.8323	$241.83	$241.85	$241.80
7 purchase totals =	$1,083.05		$1,180.0077	$1,180.00	$1,180.05	$1,179.80