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	$103.41	7.849%	$111.5267	$111.53	$111.55	$111.50
Purchase #2	$70.63	10.297%	$77.9028	$77.90	$77.90	$77.90
Purchase #3	$44.62	9.185%	$48.7183	$48.72	$48.70	$48.70
Purchase #4	$214.88	9.802%	$235.9425	$235.94	$235.95	$235.90
Purchase #5	$124.46	12.115%	$139.5383	$139.54	$139.55	$139.50
Purchase #6	$232.67	7.294%	$249.6409	$249.64	$249.65	$249.60
Purchase #7	$54.64	9.730%	$59.9565	$59.96	$59.95	$60.00
7 purchase totals =	$845.31		$923.2260	$923.23	$923.25	$923.10