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	$94.64	6.524%	$100.8143	$100.81	$100.80	$100.80
Purchase #2	$73.95	8.673%	$80.3637	$80.36	$80.35	$80.40
Purchase #3	$20.61	3.496%	$21.3305	$21.33	$21.35	$21.30
Purchase #4	$236.90	12.244%	$265.906	$265.91	$265.90	$265.90
Purchase #5	$149.87	9.820%	$164.5872	$164.59	$164.60	$164.60
Purchase #6	$171.63	9.667%	$188.2215	$188.22	$188.20	$188.20
Purchase #7	$124.48	12.659%	$140.2379	$140.24	$140.25	$140.20
7 purchase totals =	$872.08		$961.4611	$961.46	$961.45	$961.40