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	$57.98	11.123%	$64.4291	$64.43	$64.45	$64.40
Purchase #2	$83.96	10.180%	$92.5071	$92.51	$92.50	$92.50
Purchase #3	$222.38	9.656%	$243.853	$243.85	$243.85	$243.90
Purchase #4	$36.56	10.119%	$40.2595	$40.26	$40.25	$40.30
Purchase #5	$242.92	10.525%	$268.4873	$268.49	$268.50	$268.50
Purchase #6	$135.50	8.353%	$146.8183	$146.82	$146.80	$146.80
Purchase #7	$217.54	7.547%	$233.9577	$233.96	$233.95	$234.00
7 purchase totals =	$996.84		$1,090.3120	$1,090.32	$1,090.30	$1,090.40