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	$16.85	11.273%	$18.7495	$18.75	$18.75	$18.70
Purchase #2	$89.59	3.256%	$92.5071	$92.51	$92.50	$92.50
Purchase #3	$123.56	13.783%	$140.5903	$140.59	$140.60	$140.60
Purchase #4	$216.89	7.685%	$233.558	$233.56	$233.55	$233.60
Purchase #5	$21.52	7.459%	$23.1252	$23.13	$23.15	$23.10
Purchase #6	$134.33	10.744%	$148.7624	$148.76	$148.75	$148.80
Purchase #7	$246.60	7.222%	$264.4095	$264.41	$264.40	$264.40
7 purchase totals =	$849.34		$921.7020	$921.71	$921.70	$921.70