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	$100.53	8.742%	$109.3183	$109.32	$109.30	$109.30
Purchase #2	$192.98	11.835%	$215.8192	$215.82	$215.80	$215.80
Purchase #3	$149.97	5.342%	$157.9814	$157.98	$158.00	$158.00
Purchase #4	$220.64	9.133%	$240.7911	$240.79	$240.80	$240.80
Purchase #5	$97.82	13.444%	$110.9709	$110.97	$110.95	$111.00
Purchase #6	$118.49	5.483%	$124.9868	$124.99	$125.00	$125.00
Purchase #7	$55.39	7.498%	$59.5431	$59.54	$59.55	$59.50
7 purchase totals =	$935.82		$1,019.4108	$1,019.41	$1,019.40	$1,019.40