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	$27.98	11.598%	$31.2251	$31.23	$31.25	$31.20
Purchase #2	$14.94	3.226%	$15.422	$15.42	$15.40	$15.40
Purchase #3	$194.89	10.590%	$215.5289	$215.53	$215.55	$215.50
Purchase #4	$168.48	12.704%	$189.8837	$189.88	$189.90	$189.90
Purchase #5	$209.51	7.410%	$225.0347	$225.03	$225.05	$225.00
Purchase #6	$37.54	6.346%	$39.9223	$39.92	$39.90	$39.90
Purchase #7	$27.74	4.155%	$28.8926	$28.89	$28.90	$28.90
7 purchase totals =	$681.08		$745.9093	$745.90	$745.95	$745.80