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	$85.46	7.341%	$91.7336	$91.73	$91.75	$91.70
Purchase #2	$140.49	7.187%	$150.587	$150.59	$150.60	$150.60
Purchase #3	$21.46	3.654%	$22.2441	$22.24	$22.25	$22.20
Purchase #4	$249.83	12.763%	$281.7158	$281.72	$281.70	$281.70
Purchase #5	$215.30	4.700%	$225.4191	$225.42	$225.40	$225.40
Purchase #6	$64.98	11.482%	$72.441	$72.44	$72.45	$72.40
Purchase #7	$59.93	7.481%	$64.4134	$64.41	$64.40	$64.40
7 purchase totals =	$837.45		$908.5540	$908.55	$908.55	$908.40