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	$183.68	3.284%	$189.7121	$189.71	$189.70	$189.70
Purchase #2	$86.30	7.592%	$92.8519	$92.85	$92.85	$92.90
Purchase #3	$135.38	11.138%	$150.4586	$150.46	$150.45	$150.50
Purchase #4	$31.84	3.712%	$33.0219	$33.02	$33.00	$33.00
Purchase #5	$70.49	11.790%	$78.8008	$78.80	$78.80	$78.80
Purchase #6	$92.57	11.542%	$103.2544	$103.25	$103.25	$103.30
Purchase #7	$26.31	3.256%	$27.1667	$27.17	$27.15	$27.20
7 purchase totals =	$626.57		$675.2664	$675.26	$675.20	$675.40