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	$19.79	5.646%	$20.9073	$20.91	$20.90	$20.90
Purchase #2	$75.39	4.217%	$78.5692	$78.57	$78.55	$78.60
Purchase #3	$51.54	11.240%	$57.3331	$57.33	$57.35	$57.30
Purchase #4	$120.50	13.774%	$137.0977	$137.10	$137.10	$137.10
Purchase #5	$40.81	3.790%	$42.3567	$42.36	$42.35	$42.40
Purchase #6	$75.85	11.537%	$84.6008	$84.60	$84.60	$84.60
Purchase #7	$200.73	6.132%	$213.0388	$213.04	$213.05	$213.00
7 purchase totals =	$584.61		$633.9036	$633.91	$633.90	$633.90