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	$69.95	13.701%	$79.5338	$79.53	$79.55	$79.50
Purchase #2	$63.66	13.841%	$72.4712	$72.47	$72.45	$72.50
Purchase #3	$130.35	3.401%	$134.7832	$134.78	$134.80	$134.80
Purchase #4	$78.77	13.219%	$89.1826	$89.18	$89.20	$89.20
Purchase #5	$168.25	13.516%	$190.9907	$190.99	$191.00	$191.00
Purchase #6	$171.69	11.786%	$191.9254	$191.93	$191.95	$191.90
Purchase #7	$67.48	6.451%	$71.8331	$71.83	$71.85	$71.80
7 purchase totals =	$750.15		$830.7200	$830.71	$830.80	$830.70