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	$125.98	13.417%	$142.8827	$142.88	$142.90	$142.90
Purchase #2	$33.90	10.715%	$37.5324	$37.53	$37.55	$37.50
Purchase #3	$166.63	8.582%	$180.9302	$180.93	$180.95	$180.90
Purchase #4	$63.74	13.237%	$72.1773	$72.18	$72.20	$72.20
Purchase #5	$36.43	5.519%	$38.4406	$38.44	$38.45	$38.40
Purchase #6	$140.91	5.179%	$148.2077	$148.21	$148.20	$148.20
Purchase #7	$181.45	12.358%	$203.8736	$203.87	$203.85	$203.90
7 purchase totals =	$749.04		$824.0445	$824.04	$824.10	$824.00