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	$76.86	5.461%	$81.0573	$81.06	$81.05	$81.10
Purchase #2	$121.73	12.182%	$136.5591	$136.56	$136.55	$136.60
Purchase #3	$73.41	6.741%	$78.3586	$78.36	$78.35	$78.40
Purchase #4	$242.49	11.442%	$270.2357	$270.24	$270.25	$270.20
Purchase #5	$75.51	13.107%	$85.4071	$85.41	$85.40	$85.40
Purchase #6	$198.55	10.263%	$218.9272	$218.93	$218.95	$218.90
Purchase #7	$231.34	11.664%	$258.3235	$258.32	$258.30	$258.30
7 purchase totals =	$1,019.89		$1,128.8685	$1,128.88	$1,128.85	$1,128.90