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	$139.95	3.749%	$145.1967	$145.20	$145.20	$145.20
Purchase #2	$208.58	9.173%	$227.713	$227.71	$227.70	$227.70
Purchase #3	$81.49	10.272%	$89.8607	$89.86	$89.85	$89.90
Purchase #4	$201.92	10.138%	$222.3906	$222.39	$222.40	$222.40
Purchase #5	$134.26	12.872%	$151.5419	$151.54	$151.55	$151.50
Purchase #6	$93.73	5.437%	$98.8261	$98.83	$98.85	$98.80
Purchase #7	$66.73	12.148%	$74.8364	$74.84	$74.85	$74.80
7 purchase totals =	$926.66		$1,010.3654	$1,010.37	$1,010.40	$1,010.30