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	$156.29	12.220%	$175.3886	$175.39	$175.40	$175.40
Purchase #2	$87.49	8.323%	$94.7718	$94.77	$94.75	$94.80
Purchase #3	$171.50	11.659%	$191.4952	$191.50	$191.50	$191.50
Purchase #4	$182.31	12.330%	$204.7888	$204.79	$204.80	$204.80
Purchase #5	$64.70	12.465%	$72.7649	$72.76	$72.75	$72.80
Purchase #6	$66.86	7.465%	$71.8511	$71.85	$71.85	$71.90
Purchase #7	$43.43	12.528%	$48.8709	$48.87	$48.85	$48.90
7 purchase totals =	$772.58		$859.9313	$859.93	$859.90	$860.10