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	$128.58	6.644%	$137.1229	$137.12	$137.10	$137.10
Purchase #2	$241.49	8.421%	$261.8259	$261.83	$261.85	$261.80
Purchase #3	$145.38	5.158%	$152.8787	$152.88	$152.90	$152.90
Purchase #4	$96.36	7.834%	$103.9088	$103.91	$103.90	$103.90
Purchase #5	$39.25	10.717%	$43.4564	$43.46	$43.45	$43.50
Purchase #6	$195.40	9.154%	$213.2869	$213.29	$213.30	$213.30
Purchase #7	$190.98	12.770%	$215.3681	$215.37	$215.35	$215.40
7 purchase totals =	$1,037.44		$1,127.8477	$1,127.86	$1,127.85	$1,127.90