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	$242.34	5.580%	$255.8626	$255.86	$255.85	$255.90
Purchase #2	$31.79	4.533%	$33.231	$33.23	$33.25	$33.20
Purchase #3	$148.91	4.482%	$155.5841	$155.58	$155.60	$155.60
Purchase #4	$202.63	3.160%	$209.0331	$209.03	$209.05	$209.00
Purchase #5	$73.32	6.220%	$77.8805	$77.88	$77.90	$77.90
Purchase #6	$94.26	11.371%	$104.9783	$104.98	$105.00	$105.00
Purchase #7	$173.85	6.260%	$184.733	$184.73	$184.75	$184.70
7 purchase totals =	$967.10		$1,021.3026	$1,021.29	$1,021.40	$1,021.30