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	$198.55	12.779%	$223.9227	$223.92	$223.90	$223.90
Purchase #2	$55.41	8.427%	$60.0794	$60.08	$60.10	$60.10
Purchase #3	$191.74	8.725%	$208.4693	$208.47	$208.45	$208.50
Purchase #4	$104.61	4.267%	$109.0737	$109.07	$109.05	$109.10
Purchase #5	$82.74	8.603%	$89.8581	$89.86	$89.85	$89.90
Purchase #6	$63.58	7.786%	$68.5303	$68.53	$68.55	$68.50
Purchase #7	$92.67	7.372%	$99.5016	$99.50	$99.50	$99.50
7 purchase totals =	$789.30		$859.4351	$859.43	$859.40	$859.50