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	$221.97	9.744%	$243.5988	$243.60	$243.60	$243.60
Purchase #2	$144.96	10.807%	$160.6258	$160.63	$160.65	$160.60
Purchase #3	$81.99	12.641%	$92.3544	$92.35	$92.35	$92.40
Purchase #4	$246.75	12.846%	$278.4475	$278.45	$278.45	$278.40
Purchase #5	$156.82	11.636%	$175.0676	$175.07	$175.05	$175.10
Purchase #6	$53.98	10.191%	$59.4811	$59.48	$59.50	$59.50
Purchase #7	$20.54	4.868%	$21.5399	$21.54	$21.55	$21.50
7 purchase totals =	$927.01		$1,031.1151	$1,031.12	$1,031.15	$1,031.10