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	$7.59	3.472%	$7.8535	$7.85	$7.85	$7.90
Purchase #2	$86.81	9.673%	$95.2071	$95.21	$95.20	$95.20
Purchase #3	$198.43	13.396%	$225.0117	$225.01	$225.00	$225.00
Purchase #4	$85.89	12.188%	$96.3583	$96.36	$96.35	$96.40
Purchase #5	$61.34	4.737%	$64.2457	$64.25	$64.25	$64.20
Purchase #6	$79.38	10.744%	$87.9086	$87.91	$87.90	$87.90
Purchase #7	$66.43	7.663%	$71.5205	$71.52	$71.50	$71.50
7 purchase totals =	$585.87		$648.1054	$648.11	$648.05	$648.10