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	$79.47	12.850%	$89.6819	$89.68	$89.70	$89.70
Purchase #2	$35.93	10.290%	$39.6272	$39.63	$39.65	$39.60
Purchase #3	$234.73	6.659%	$250.3607	$250.36	$250.35	$250.40
Purchase #4	$82.94	9.346%	$90.6916	$90.69	$90.70	$90.70
Purchase #5	$104.43	3.465%	$108.0485	$108.05	$108.05	$108.00
Purchase #6	$247.62	4.379%	$258.4633	$258.46	$258.45	$258.50
Purchase #7	$150.98	11.673%	$168.6039	$168.60	$168.60	$168.60
7 purchase totals =	$936.10		$1,005.4771	$1,005.47	$1,005.50	$1,005.50