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	$227.36	12.564%	$255.9255	$255.93	$255.95	$255.90
Purchase #2	$67.72	8.406%	$73.4125	$73.41	$73.40	$73.40
Purchase #3	$81.82	13.552%	$92.9082	$92.91	$92.90	$92.90
Purchase #4	$233.97	10.380%	$258.2561	$258.26	$258.25	$258.30
Purchase #5	$5.81	13.165%	$6.5749	$6.57	$6.55	$6.60
Purchase #6	$232.61	9.351%	$254.3614	$254.36	$254.35	$254.40
Purchase #7	$249.96	3.785%	$259.421	$259.42	$259.40	$259.40
7 purchase totals =	$1,099.25		$1,200.8596	$1,200.86	$1,200.80	$1,200.90