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	$246.46	10.738%	$272.9249	$272.92	$272.90	$272.90
Purchase #2	$189.83	3.654%	$196.7664	$196.77	$196.75	$196.80
Purchase #3	$243.38	7.456%	$261.5264	$261.53	$261.55	$261.50
Purchase #4	$238.85	6.673%	$254.7885	$254.79	$254.80	$254.80
Purchase #5	$88.87	7.664%	$95.681	$95.68	$95.70	$95.70
Purchase #6	$83.89	10.121%	$92.3805	$92.38	$92.40	$92.40
Purchase #7	$124.91	11.606%	$139.4071	$139.41	$139.40	$139.40
7 purchase totals =	$1,216.19		$1,313.4748	$1,313.48	$1,313.50	$1,313.50