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	$175.35	7.135%	$187.8612	$187.86	$187.85	$187.90
Purchase #2	$102.77	13.415%	$116.5566	$116.56	$116.55	$116.60
Purchase #3	$164.80	3.228%	$170.1197	$170.12	$170.10	$170.10
Purchase #4	$38.60	6.842%	$41.241	$41.24	$41.25	$41.20
Purchase #5	$52.76	12.813%	$59.5201	$59.52	$59.50	$59.50
Purchase #6	$234.77	3.129%	$242.116	$242.12	$242.10	$242.10
Purchase #7	$250.97	9.399%	$274.5587	$274.56	$274.55	$274.60
7 purchase totals =	$1,020.02		$1,091.9733	$1,091.98	$1,091.90	$1,092.00