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	$137.49	12.395%	$154.5319	$154.53	$154.55	$154.50
Purchase #2	$83.44	7.427%	$89.6371	$89.64	$89.65	$89.60
Purchase #3	$101.87	7.397%	$109.4053	$109.41	$109.40	$109.40
Purchase #4	$68.62	6.270%	$72.9225	$72.92	$72.90	$72.90
Purchase #5	$69.49	12.138%	$77.9247	$77.92	$77.90	$77.90
Purchase #6	$10.79	13.735%	$12.272	$12.27	$12.25	$12.30
Purchase #7	$169.29	11.336%	$188.4807	$188.48	$188.50	$188.50
7 purchase totals =	$640.99		$705.1742	$705.17	$705.15	$705.10