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	$63.66	6.638%	$67.8858	$67.89	$67.90	$67.90
Purchase #2	$210.37	10.457%	$232.3684	$232.37	$232.35	$232.40
Purchase #3	$204.42	9.316%	$223.4638	$223.46	$223.45	$223.50
Purchase #4	$58.78	13.655%	$66.8064	$66.81	$66.80	$66.80
Purchase #5	$122.90	10.464%	$135.7603	$135.76	$135.75	$135.80
Purchase #6	$86.48	3.680%	$89.6625	$89.66	$89.65	$89.70
Purchase #7	$146.66	12.802%	$165.4354	$165.44	$165.45	$165.40
7 purchase totals =	$893.27		$981.3826	$981.39	$981.35	$981.50