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	$98.93	3.650%	$102.5409	$102.54	$102.55	$102.50
Purchase #2	$215.28	10.640%	$238.1858	$238.19	$238.20	$238.20
Purchase #3	$80.40	9.769%	$88.2543	$88.25	$88.25	$88.30
Purchase #4	$247.82	8.843%	$269.7347	$269.73	$269.75	$269.70
Purchase #5	$67.46	7.609%	$72.593	$72.59	$72.60	$72.60
Purchase #6	$240.46	12.766%	$271.1571	$271.16	$271.15	$271.20
Purchase #7	$103.73	10.263%	$114.3758	$114.38	$114.40	$114.40
7 purchase totals =	$1,054.08		$1,156.8416	$1,156.84	$1,156.90	$1,156.90