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	$19.77	3.681%	$20.4977	$20.50	$20.50	$20.50
Purchase #2	$75.92	3.331%	$78.4489	$78.45	$78.45	$78.40
Purchase #3	$89.52	7.662%	$96.379	$96.38	$96.40	$96.40
Purchase #4	$52.78	12.488%	$59.3712	$59.37	$59.35	$59.40
Purchase #5	$162.37	7.407%	$174.3967	$174.40	$174.40	$174.40
Purchase #6	$26.62	8.696%	$28.9349	$28.93	$28.95	$28.90
Purchase #7	$223.86	5.646%	$236.4991	$236.50	$236.50	$236.50
7 purchase totals =	$650.84		$694.5275	$694.53	$694.55	$694.50