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	$19.95	6.741%	$21.2948	$21.29	$21.30	$21.30
Purchase #2	$210.96	3.495%	$218.3331	$218.33	$218.35	$218.30
Purchase #3	$84.94	7.863%	$91.6188	$91.62	$91.60	$91.60
Purchase #4	$166.62	5.559%	$175.8824	$175.88	$175.90	$175.90
Purchase #5	$53.36	11.824%	$59.6693	$59.67	$59.65	$59.70
Purchase #6	$243.78	10.650%	$269.7426	$269.74	$269.75	$269.70
Purchase #7	$160.88	8.192%	$174.0593	$174.06	$174.05	$174.10
7 purchase totals =	$940.49		$1,010.6003	$1,010.59	$1,010.60	$1,010.60