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	$160.45	11.448%	$178.8183	$178.82	$178.80	$178.80
Purchase #2	$232.27	11.166%	$258.2053	$258.21	$258.20	$258.20
Purchase #3	$178.37	5.735%	$188.5995	$188.60	$188.60	$188.60
Purchase #4	$110.36	13.160%	$124.8834	$124.88	$124.90	$124.90
Purchase #5	$80.51	12.812%	$90.8249	$90.82	$90.80	$90.80
Purchase #6	$162.99	5.428%	$171.8371	$171.84	$171.85	$171.80
Purchase #7	$6.79	9.595%	$7.4415	$7.44	$7.45	$7.40
7 purchase totals =	$931.74		$1,020.6100	$1,020.61	$1,020.60	$1,020.50