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	$84.27	6.276%	$89.5588	$89.56	$89.55	$89.60
Purchase #2	$192.84	8.309%	$208.8631	$208.86	$208.85	$208.90
Purchase #3	$104.46	7.604%	$112.4031	$112.40	$112.40	$112.40
Purchase #4	$116.86	7.430%	$125.5427	$125.54	$125.55	$125.50
Purchase #5	$61.42	10.527%	$67.8857	$67.89	$67.90	$67.90
Purchase #6	$205.52	6.457%	$218.7904	$218.79	$218.80	$218.80
Purchase #7	$161.94	3.428%	$167.4913	$167.49	$167.50	$167.50
7 purchase totals =	$927.31		$990.5351	$990.53	$990.55	$990.60