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	$185.94	9.654%	$203.8906	$203.89	$203.90	$203.90
Purchase #2	$161.72	6.546%	$172.3062	$172.31	$172.30	$172.30
Purchase #3	$108.94	3.811%	$113.0917	$113.09	$113.10	$113.10
Purchase #4	$41.83	5.843%	$44.2741	$44.27	$44.25	$44.30
Purchase #5	$38.80	6.556%	$41.3437	$41.34	$41.35	$41.30
Purchase #6	$131.79	10.816%	$146.0444	$146.04	$146.05	$146.00
Purchase #7	$120.50	6.306%	$128.0987	$128.10	$128.10	$128.10
7 purchase totals =	$789.52		$849.0494	$849.04	$849.05	$849.00