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	$93.36	3.596%	$96.7172	$96.72	$96.70	$96.70
Purchase #2	$78.99	13.202%	$89.4183	$89.42	$89.40	$89.40
Purchase #3	$152.63	9.508%	$167.1421	$167.14	$167.15	$167.10
Purchase #4	$231.45	3.238%	$238.9444	$238.94	$238.95	$238.90
Purchase #5	$31.75	5.727%	$33.5683	$33.57	$33.55	$33.60
Purchase #6	$76.65	11.761%	$85.6648	$85.66	$85.65	$85.70
Purchase #7	$56.58	10.354%	$62.4383	$62.44	$62.45	$62.40
7 purchase totals =	$721.41		$773.8934	$773.89	$773.85	$773.80