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	$71.33	3.540%	$73.8551	$73.86	$73.85	$73.90
Purchase #2	$143.88	11.803%	$160.8622	$160.86	$160.85	$160.90
Purchase #3	$174.25	7.308%	$186.9842	$186.98	$187.00	$187.00
Purchase #4	$164.63	3.571%	$170.5089	$170.51	$170.50	$170.50
Purchase #5	$143.59	12.735%	$161.8762	$161.88	$161.90	$161.90
Purchase #6	$175.83	13.711%	$199.9381	$199.94	$199.95	$199.90
Purchase #7	$177.83	10.308%	$196.1607	$196.16	$196.15	$196.20
7 purchase totals =	$1,051.34		$1,150.1854	$1,150.19	$1,150.20	$1,150.30