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	$232.77	6.849%	$248.7124	$248.71	$248.70	$248.70
Purchase #2	$155.28	8.591%	$168.6201	$168.62	$168.60	$168.60
Purchase #3	$241.73	6.131%	$256.5505	$256.55	$256.55	$256.60
Purchase #4	$40.64	4.310%	$42.3916	$42.39	$42.40	$42.40
Purchase #5	$125.84	7.559%	$135.3522	$135.35	$135.35	$135.40
Purchase #6	$57.99	11.410%	$64.6067	$64.61	$64.60	$64.60
Purchase #7	$89.53	12.627%	$100.835	$100.84	$100.85	$100.80
7 purchase totals =	$943.78		$1,017.0685	$1,017.07	$1,017.05	$1,017.10