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	$169.70	10.249%	$187.0926	$187.09	$187.10	$187.10
Purchase #2	$39.96	6.835%	$42.6913	$42.69	$42.70	$42.70
Purchase #3	$173.73	8.686%	$188.8202	$188.82	$188.80	$188.80
Purchase #4	$38.62	8.760%	$42.0031	$42.00	$42.00	$42.00
Purchase #5	$217.34	7.695%	$234.0643	$234.06	$234.05	$234.10
Purchase #6	$168.36	6.392%	$179.1216	$179.12	$179.10	$179.10
Purchase #7	$65.86	8.385%	$71.3824	$71.38	$71.40	$71.40
7 purchase totals =	$873.57		$945.1755	$945.16	$945.15	$945.20