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	$122.38	11.257%	$136.1563	$136.16	$136.15	$136.20
Purchase #2	$39.56	4.239%	$41.2369	$41.24	$41.25	$41.20
Purchase #3	$227.68	6.281%	$241.9806	$241.98	$242.00	$242.00
Purchase #4	$208.79	11.585%	$232.9783	$232.98	$233.00	$233.00
Purchase #5	$111.59	4.143%	$116.2132	$116.21	$116.20	$116.20
Purchase #6	$80.48	6.730%	$85.8963	$85.90	$85.90	$85.90
Purchase #7	$137.26	9.556%	$150.3766	$150.38	$150.40	$150.40
7 purchase totals =	$927.74		$1,004.8382	$1,004.85	$1,004.90	$1,004.90