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	$171.69	10.710%	$190.078	$190.08	$190.10	$190.10
Purchase #2	$118.80	12.340%	$133.4599	$133.46	$133.45	$133.50
Purchase #3	$96.46	13.850%	$109.8197	$109.82	$109.80	$109.80
Purchase #4	$84.77	10.139%	$93.3648	$93.36	$93.35	$93.40
Purchase #5	$172.46	13.747%	$196.1681	$196.17	$196.15	$196.20
Purchase #6	$120.87	3.828%	$125.4969	$125.50	$125.50	$125.50
Purchase #7	$77.87	13.710%	$88.546	$88.55	$88.55	$88.50
7 purchase totals =	$842.92		$936.9334	$936.94	$936.90	$937.00