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	$245.54	4.864%	$257.4831	$257.48	$257.50	$257.50
Purchase #2	$114.33	4.861%	$119.8876	$119.89	$119.90	$119.90
Purchase #3	$75.32	4.423%	$78.6514	$78.65	$78.65	$78.70
Purchase #4	$234.71	3.813%	$243.6595	$243.66	$243.65	$243.70
Purchase #5	$77.74	10.814%	$86.1468	$86.15	$86.15	$86.10
Purchase #6	$30.60	8.536%	$33.212	$33.21	$33.20	$33.20
Purchase #7	$154.62	3.346%	$159.7936	$159.79	$159.80	$159.80
7 purchase totals =	$932.86		$978.8340	$978.83	$978.85	$978.90