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	$223.89	6.108%	$237.5652	$237.57	$237.55	$237.60
Purchase #2	$72.78	6.682%	$77.6432	$77.64	$77.65	$77.60
Purchase #3	$83.74	6.702%	$89.3523	$89.35	$89.35	$89.40
Purchase #4	$78.60	3.515%	$81.3628	$81.36	$81.35	$81.40
Purchase #5	$92.64	8.694%	$100.6941	$100.69	$100.70	$100.70
Purchase #6	$243.73	7.863%	$262.8945	$262.89	$262.90	$262.90
Purchase #7	$7.77	5.600%	$8.2051	$8.21	$8.20	$8.20
7 purchase totals =	$803.15		$857.7172	$857.71	$857.70	$857.80