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	$93.71	6.590%	$99.8855	$99.89	$99.90	$99.90
Purchase #2	$180.60	4.262%	$188.2972	$188.30	$188.30	$188.30
Purchase #3	$93.29	3.787%	$96.8229	$96.82	$96.80	$96.80
Purchase #4	$213.57	9.115%	$233.0369	$233.04	$233.05	$233.00
Purchase #5	$154.62	3.186%	$159.5462	$159.55	$159.55	$159.50
Purchase #6	$76.38	8.348%	$82.7562	$82.76	$82.75	$82.80
Purchase #7	$203.27	9.270%	$222.1131	$222.11	$222.10	$222.10
7 purchase totals =	$1,015.44		$1,082.4580	$1,082.47	$1,082.45	$1,082.40