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	$203.96	13.155%	$230.7909	$230.79	$230.80	$230.80
Purchase #2	$168.48	6.489%	$179.4127	$179.41	$179.40	$179.40
Purchase #3	$55.77	11.526%	$62.1981	$62.20	$62.20	$62.20
Purchase #4	$233.56	13.564%	$265.2401	$265.24	$265.25	$265.20
Purchase #5	$211.49	11.744%	$236.3274	$236.33	$236.35	$236.30
Purchase #6	$207.53	13.155%	$234.8306	$234.83	$234.85	$234.80
Purchase #7	$98.72	13.282%	$111.832	$111.83	$111.85	$111.80
7 purchase totals =	$1,179.51		$1,320.6318	$1,320.63	$1,320.70	$1,320.50