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	$38.58	4.819%	$40.4392	$40.44	$40.45	$40.40
Purchase #2	$218.37	11.293%	$243.0305	$243.03	$243.05	$243.00
Purchase #3	$190.65	9.151%	$208.0964	$208.10	$208.10	$208.10
Purchase #4	$156.64	7.870%	$168.9676	$168.97	$168.95	$169.00
Purchase #5	$42.94	11.531%	$47.8914	$47.89	$47.90	$47.90
Purchase #6	$53.26	6.243%	$56.585	$56.59	$56.60	$56.60
Purchase #7	$67.29	7.116%	$72.0784	$72.08	$72.10	$72.10
7 purchase totals =	$767.73		$837.0885	$837.10	$837.15	$837.10