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	$128.61	6.452%	$136.9079	$136.91	$136.90	$136.90
Purchase #2	$28.80	10.349%	$31.7805	$31.78	$31.80	$31.80
Purchase #3	$45.75	11.181%	$50.8653	$50.87	$50.85	$50.90
Purchase #4	$200.99	10.849%	$222.7954	$222.80	$222.80	$222.80
Purchase #5	$162.36	12.560%	$182.7524	$182.75	$182.75	$182.80
Purchase #6	$68.82	13.604%	$78.1823	$78.18	$78.20	$78.20
Purchase #7	$93.63	6.170%	$99.407	$99.41	$99.40	$99.40
7 purchase totals =	$728.96		$802.6908	$802.70	$802.70	$802.80