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	$70.96	10.218%	$78.2107	$78.21	$78.20	$78.20
Purchase #2	$246.76	11.790%	$275.853	$275.85	$275.85	$275.90
Purchase #3	$185.88	12.688%	$209.4645	$209.46	$209.45	$209.50
Purchase #4	$82.51	8.191%	$89.2684	$89.27	$89.25	$89.30
Purchase #5	$160.30	6.322%	$170.4342	$170.43	$170.45	$170.40
Purchase #6	$154.61	9.184%	$168.8094	$168.81	$168.80	$168.80
Purchase #7	$163.88	8.454%	$177.7344	$177.73	$177.75	$177.70
7 purchase totals =	$1,064.90		$1,169.7746	$1,169.76	$1,169.75	$1,169.80