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	$244.37	10.276%	$269.4815	$269.48	$269.50	$269.50
Purchase #2	$156.69	6.112%	$166.2669	$166.27	$166.25	$166.30
Purchase #3	$205.25	3.380%	$212.1875	$212.19	$212.20	$212.20
Purchase #4	$69.55	9.296%	$76.0154	$76.02	$76.00	$76.00
Purchase #5	$170.35	6.494%	$181.4125	$181.41	$181.40	$181.40
Purchase #6	$69.46	4.768%	$72.7719	$72.77	$72.75	$72.80
Purchase #7	$54.67	8.273%	$59.1928	$59.19	$59.20	$59.20
7 purchase totals =	$970.34		$1,037.3285	$1,037.33	$1,037.30	$1,037.40