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	$38.75	8.441%	$42.0209	$42.02	$42.00	$42.00
Purchase #2	$145.67	4.661%	$152.4597	$152.46	$152.45	$152.50
Purchase #3	$57.61	10.815%	$63.8405	$63.84	$63.85	$63.80
Purchase #4	$210.41	12.506%	$236.7239	$236.72	$236.70	$236.70
Purchase #5	$229.50	13.138%	$259.6517	$259.65	$259.65	$259.70
Purchase #6	$247.53	6.841%	$264.4635	$264.46	$264.45	$264.50
Purchase #7	$11.49	3.474%	$11.8892	$11.89	$11.90	$11.90
7 purchase totals =	$940.96		$1,031.0494	$1,031.04	$1,031.00	$1,031.10