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	$39.49	8.450%	$42.8269	$42.83	$42.85	$42.80
Purchase #2	$39.79	9.502%	$43.5708	$43.57	$43.55	$43.60
Purchase #3	$135.25	5.275%	$142.3844	$142.38	$142.40	$142.40
Purchase #4	$250.83	9.600%	$274.9097	$274.91	$274.90	$274.90
Purchase #5	$186.41	7.698%	$200.7598	$200.76	$200.75	$200.80
Purchase #6	$147.86	9.818%	$162.3769	$162.38	$162.40	$162.40
Purchase #7	$78.93	7.519%	$84.8647	$84.86	$84.85	$84.90
7 purchase totals =	$878.56		$951.6932	$951.69	$951.70	$951.80