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	$71.69	8.177%	$77.5521	$77.55	$77.55	$77.60
Purchase #2	$64.27	4.303%	$67.0355	$67.04	$67.05	$67.00
Purchase #3	$113.41	8.767%	$123.3527	$123.35	$123.35	$123.40
Purchase #4	$40.64	4.306%	$42.39	$42.39	$42.40	$42.40
Purchase #5	$187.28	11.366%	$208.5662	$208.57	$208.55	$208.60
Purchase #6	$189.69	12.231%	$212.891	$212.89	$212.90	$212.90
Purchase #7	$124.43	5.835%	$131.6905	$131.69	$131.70	$131.70
7 purchase totals =	$791.41		$863.4780	$863.48	$863.50	$863.60