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	$52.88	12.803%	$59.6502	$59.65	$59.65	$59.70
Purchase #2	$249.46	3.782%	$258.8946	$258.89	$258.90	$258.90
Purchase #3	$73.33	12.151%	$82.2403	$82.24	$82.25	$82.20
Purchase #4	$232.69	7.543%	$250.2418	$250.24	$250.25	$250.20
Purchase #5	$125.31	10.737%	$138.7645	$138.76	$138.75	$138.80
Purchase #6	$126.98	10.610%	$140.4526	$140.45	$140.45	$140.50
Purchase #7	$166.31	9.284%	$181.7502	$181.75	$181.75	$181.80
7 purchase totals =	$1,026.96		$1,111.9942	$1,111.98	$1,112.00	$1,112.10