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	$142.31	4.280%	$148.4009	$148.40	$148.40	$148.40
Purchase #2	$27.39	3.390%	$28.3185	$28.32	$28.30	$28.30
Purchase #3	$73.83	9.516%	$80.8557	$80.86	$80.85	$80.90
Purchase #4	$70.94	10.645%	$78.4916	$78.49	$78.50	$78.50
Purchase #5	$154.50	4.829%	$161.9608	$161.96	$161.95	$162.00
Purchase #6	$174.25	3.281%	$179.9671	$179.97	$179.95	$180.00
Purchase #7	$133.38	11.635%	$148.8988	$148.90	$148.90	$148.90
7 purchase totals =	$776.60		$826.8934	$826.90	$826.85	$827.00