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	$37.98	11.296%	$42.2702	$42.27	$42.25	$42.30
Purchase #2	$250.52	9.583%	$274.5273	$274.53	$274.55	$274.50
Purchase #3	$99.62	3.400%	$103.0071	$103.01	$103.00	$103.00
Purchase #4	$41.40	3.274%	$42.7554	$42.76	$42.75	$42.80
Purchase #5	$7.59	3.840%	$7.8815	$7.88	$7.90	$7.90
Purchase #6	$133.48	12.276%	$149.866	$149.87	$149.85	$149.90
Purchase #7	$168.45	11.133%	$187.2035	$187.20	$187.20	$187.20
7 purchase totals =	$739.04		$807.5110	$807.52	$807.50	$807.60