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	$80.78	3.624%	$83.7075	$83.71	$83.70	$83.70
Purchase #2	$212.42	6.439%	$226.0977	$226.10	$226.10	$226.10
Purchase #3	$186.87	5.179%	$196.548	$196.55	$196.55	$196.50
Purchase #4	$81.70	10.633%	$90.3872	$90.39	$90.40	$90.40
Purchase #5	$102.31	6.424%	$108.8824	$108.88	$108.90	$108.90
Purchase #6	$75.35	10.641%	$83.368	$83.37	$83.35	$83.40
Purchase #7	$191.51	10.807%	$212.2065	$212.21	$212.20	$212.20
7 purchase totals =	$930.94		$1,001.1973	$1,001.21	$1,001.20	$1,001.20