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	$47.79	7.289%	$51.2734	$51.27	$51.25	$51.30
Purchase #2	$174.67	12.695%	$196.8444	$196.84	$196.85	$196.80
Purchase #3	$243.98	12.259%	$273.8895	$273.89	$273.90	$273.90
Purchase #4	$166.43	7.265%	$178.5211	$178.52	$178.50	$178.50
Purchase #5	$82.97	12.469%	$93.3155	$93.32	$93.30	$93.30
Purchase #6	$227.70	11.861%	$254.7075	$254.71	$254.70	$254.70
Purchase #7	$122.29	12.596%	$137.6936	$137.69	$137.70	$137.70
7 purchase totals =	$1,065.83		$1,186.2450	$1,186.24	$1,186.20	$1,186.20