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	$62.76	12.456%	$70.5774	$70.58	$70.60	$70.60
Purchase #2	$78.88	9.274%	$86.1953	$86.20	$86.20	$86.20
Purchase #3	$215.77	7.402%	$231.7413	$231.74	$231.75	$231.70
Purchase #4	$66.89	7.799%	$72.1068	$72.11	$72.10	$72.10
Purchase #5	$39.70	6.346%	$42.2194	$42.22	$42.20	$42.20
Purchase #6	$66.28	8.358%	$71.8197	$71.82	$71.80	$71.80
Purchase #7	$33.66	5.558%	$35.5308	$35.53	$35.55	$35.50
7 purchase totals =	$563.94		$610.1907	$610.20	$610.20	$610.10