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	$64.94	9.602%	$71.1755	$71.18	$71.20	$71.20
Purchase #2	$66.68	9.338%	$72.9066	$72.91	$72.90	$72.90
Purchase #3	$189.95	8.542%	$206.1755	$206.18	$206.20	$206.20
Purchase #4	$106.65	13.289%	$120.8227	$120.82	$120.80	$120.80
Purchase #5	$91.39	10.346%	$100.8452	$100.85	$100.85	$100.80
Purchase #6	$80.78	5.606%	$85.3085	$85.31	$85.30	$85.30
Purchase #7	$245.34	7.766%	$264.3931	$264.39	$264.40	$264.40
7 purchase totals =	$845.73		$921.6271	$921.64	$921.65	$921.60