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	$92.43	11.609%	$103.1602	$103.16	$103.15	$103.20
Purchase #2	$243.49	11.361%	$271.1529	$271.15	$271.15	$271.20
Purchase #3	$6.85	7.121%	$7.3378	$7.34	$7.35	$7.30
Purchase #4	$60.86	11.560%	$67.8954	$67.90	$67.90	$67.90
Purchase #5	$183.50	8.705%	$199.4737	$199.47	$199.45	$199.50
Purchase #6	$19.61	8.132%	$21.2047	$21.20	$21.20	$21.20
Purchase #7	$28.75	9.434%	$31.4623	$31.46	$31.45	$31.50
7 purchase totals =	$635.49		$701.6870	$701.68	$701.65	$701.80