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	$201.79	9.619%	$221.2002	$221.20	$221.20	$221.20
Purchase #2	$67.80	5.423%	$71.4768	$71.48	$71.50	$71.50
Purchase #3	$8.47	4.266%	$8.8313	$8.83	$8.85	$8.80
Purchase #4	$42.29	10.690%	$46.8108	$46.81	$46.80	$46.80
Purchase #5	$178.82	3.360%	$184.8284	$184.83	$184.85	$184.80
Purchase #6	$156.38	7.645%	$168.3353	$168.34	$168.35	$168.30
Purchase #7	$130.71	9.319%	$142.8909	$142.89	$142.90	$142.90
7 purchase totals =	$786.26		$844.3737	$844.38	$844.45	$844.30