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	$212.26	10.821%	$235.2287	$235.23	$235.25	$235.20
Purchase #2	$193.91	12.533%	$218.2127	$218.21	$218.20	$218.20
Purchase #3	$108.72	7.448%	$116.8175	$116.82	$116.80	$116.80
Purchase #4	$47.70	13.610%	$54.192	$54.19	$54.20	$54.20
Purchase #5	$33.88	11.802%	$37.8785	$37.88	$37.90	$37.90
Purchase #6	$59.63	13.231%	$67.5196	$67.52	$67.50	$67.50
Purchase #7	$114.94	11.524%	$128.1857	$128.19	$128.20	$128.20
7 purchase totals =	$771.04		$858.0347	$858.04	$858.05	$858.00