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	$61.89	4.292%	$64.5463	$64.55	$64.55	$64.50
Purchase #2	$80.39	6.110%	$85.3018	$85.30	$85.30	$85.30
Purchase #3	$75.41	9.812%	$82.8092	$82.81	$82.80	$82.80
Purchase #4	$5.93	5.178%	$6.2371	$6.24	$6.25	$6.20
Purchase #5	$30.91	5.515%	$32.6147	$32.61	$32.60	$32.60
Purchase #6	$58.72	4.662%	$61.4575	$61.46	$61.45	$61.50
Purchase #7	$161.25	13.692%	$183.3284	$183.33	$183.35	$183.30
7 purchase totals =	$474.50		$516.2950	$516.30	$516.30	$516.20