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	$98.72	5.287%	$103.9393	$103.94	$103.95	$103.90
Purchase #2	$199.76	11.318%	$222.3688	$222.37	$222.35	$222.40
Purchase #3	$27.70	3.371%	$28.6338	$28.63	$28.65	$28.60
Purchase #4	$168.61	6.365%	$179.342	$179.34	$179.35	$179.30
Purchase #5	$63.96	9.687%	$70.1558	$70.16	$70.15	$70.20
Purchase #6	$137.55	12.586%	$154.862	$154.86	$154.85	$154.90
Purchase #7	$129.59	3.508%	$134.136	$134.14	$134.15	$134.10
7 purchase totals =	$825.89		$893.4377	$893.44	$893.45	$893.40