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	$84.77	5.520%	$89.4493	$89.45	$89.45	$89.40
Purchase #2	$155.48	8.410%	$168.5559	$168.56	$168.55	$168.60
Purchase #3	$103.86	8.453%	$112.6393	$112.64	$112.65	$112.60
Purchase #4	$222.89	10.713%	$246.7682	$246.77	$246.75	$246.80
Purchase #5	$236.63	7.319%	$253.9489	$253.95	$253.95	$253.90
Purchase #6	$237.48	8.380%	$257.3808	$257.38	$257.40	$257.40
Purchase #7	$153.35	11.744%	$171.3594	$171.36	$171.35	$171.40
7 purchase totals =	$1,194.46		$1,300.1018	$1,300.11	$1,300.10	$1,300.10