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	$35.62	3.623%	$36.9105	$36.91	$36.90	$36.90
Purchase #2	$75.32	9.664%	$82.5989	$82.60	$82.60	$82.60
Purchase #3	$249.69	4.485%	$260.8886	$260.89	$260.90	$260.90
Purchase #4	$163.79	12.245%	$183.8461	$183.85	$183.85	$183.80
Purchase #5	$51.40	11.816%	$57.4734	$57.47	$57.45	$57.50
Purchase #6	$134.41	3.704%	$139.3885	$139.39	$139.40	$139.40
Purchase #7	$28.61	9.463%	$31.3174	$31.32	$31.30	$31.30
7 purchase totals =	$738.84		$792.4234	$792.43	$792.40	$792.40