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	$68.55	12.191%	$76.9069	$76.91	$76.90	$76.90
Purchase #2	$227.27	10.405%	$250.9174	$250.92	$250.90	$250.90
Purchase #3	$82.39	11.211%	$91.6267	$91.63	$91.65	$91.60
Purchase #4	$72.77	6.497%	$77.4979	$77.50	$77.50	$77.50
Purchase #5	$79.63	13.547%	$90.4175	$90.42	$90.40	$90.40
Purchase #6	$123.42	4.836%	$129.3886	$129.39	$129.40	$129.40
Purchase #7	$136.41	3.387%	$141.0302	$141.03	$141.05	$141.00
7 purchase totals =	$790.44		$857.7852	$857.80	$857.80	$857.70