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	$157.37	7.332%	$168.9084	$168.91	$168.90	$168.90
Purchase #2	$104.45	8.301%	$113.1204	$113.12	$113.10	$113.10
Purchase #3	$70.64	13.374%	$80.0874	$80.09	$80.10	$80.10
Purchase #4	$171.81	10.362%	$189.613	$189.61	$189.60	$189.60
Purchase #5	$61.81	5.793%	$65.3907	$65.39	$65.40	$65.40
Purchase #6	$25.65	12.430%	$28.8383	$28.84	$28.85	$28.80
Purchase #7	$73.30	12.744%	$82.6414	$82.64	$82.65	$82.60
7 purchase totals =	$665.03		$728.5996	$728.60	$728.60	$728.50