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	$130.46	10.506%	$144.1661	$144.17	$144.15	$144.20
Purchase #2	$105.56	12.521%	$118.7772	$118.78	$118.80	$118.80
Purchase #3	$94.56	11.225%	$105.1744	$105.17	$105.15	$105.20
Purchase #4	$86.29	8.433%	$93.5668	$93.57	$93.55	$93.60
Purchase #5	$174.35	12.179%	$195.5841	$195.58	$195.60	$195.60
Purchase #6	$248.36	10.690%	$274.9097	$274.91	$274.90	$274.90
Purchase #7	$99.52	10.264%	$109.7347	$109.73	$109.75	$109.70
7 purchase totals =	$939.10		$1,041.9130	$1,041.91	$1,041.90	$1,042.00