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	$78.46	7.629%	$84.4457	$84.45	$84.45	$84.40
Purchase #2	$90.91	3.799%	$94.3637	$94.36	$94.35	$94.40
Purchase #3	$69.71	3.489%	$72.1422	$72.14	$72.15	$72.10
Purchase #4	$247.70	13.796%	$281.8727	$281.87	$281.85	$281.90
Purchase #5	$67.29	7.202%	$72.1362	$72.14	$72.15	$72.10
Purchase #6	$42.77	6.663%	$45.6198	$45.62	$45.60	$45.60
Purchase #7	$239.77	11.720%	$267.871	$267.87	$267.85	$267.90
7 purchase totals =	$836.61		$918.4513	$918.45	$918.40	$918.40