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	$87.67	13.705%	$99.6852	$99.69	$99.70	$99.70
Purchase #2	$133.41	10.661%	$147.6328	$147.63	$147.65	$147.60
Purchase #3	$136.52	9.394%	$149.3447	$149.34	$149.35	$149.30
Purchase #4	$73.82	3.351%	$76.2937	$76.29	$76.30	$76.30
Purchase #5	$172.82	10.614%	$191.1631	$191.16	$191.15	$191.20
Purchase #6	$248.84	12.176%	$279.1388	$279.14	$279.15	$279.10
Purchase #7	$155.48	8.582%	$168.8233	$168.82	$168.80	$168.80
7 purchase totals =	$1,008.56		$1,112.0816	$1,112.07	$1,112.10	$1,112.00