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	$179.96	6.608%	$191.8518	$191.85	$191.85	$191.90
Purchase #2	$150.85	7.708%	$162.4775	$162.48	$162.50	$162.50
Purchase #3	$75.57	13.609%	$85.8543	$85.85	$85.85	$85.90
Purchase #4	$27.83	12.124%	$31.2041	$31.20	$31.20	$31.20
Purchase #5	$56.72	7.586%	$61.0228	$61.02	$61.00	$61.00
Purchase #6	$138.94	7.126%	$148.8409	$148.84	$148.85	$148.80
Purchase #7	$117.92	9.456%	$129.0705	$129.07	$129.05	$129.10
7 purchase totals =	$747.79		$810.3219	$810.31	$810.30	$810.40