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	$71.41	3.477%	$73.8929	$73.89	$73.90	$73.90
Purchase #2	$124.86	9.156%	$136.2922	$136.29	$136.30	$136.30
Purchase #3	$99.96	10.520%	$110.4758	$110.48	$110.50	$110.50
Purchase #4	$99.31	7.660%	$106.9171	$106.92	$106.90	$106.90
Purchase #5	$166.66	7.342%	$178.8962	$178.90	$178.90	$178.90
Purchase #6	$137.93	10.574%	$152.5147	$152.51	$152.50	$152.50
Purchase #7	$149.71	5.836%	$158.4471	$158.45	$158.45	$158.40
7 purchase totals =	$849.84		$917.4360	$917.44	$917.45	$917.40