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	$71.87	12.682%	$80.9846	$80.98	$81.00	$81.00
Purchase #2	$188.71	7.771%	$203.3747	$203.37	$203.35	$203.40
Purchase #3	$229.49	6.259%	$243.8538	$243.85	$243.85	$243.90
Purchase #4	$59.96	9.473%	$65.64	$65.64	$65.65	$65.60
Purchase #5	$101.35	11.428%	$112.9323	$112.93	$112.95	$112.90
Purchase #6	$119.59	12.777%	$134.87	$134.87	$134.85	$134.90
Purchase #7	$85.91	5.804%	$90.8962	$90.90	$90.90	$90.90
7 purchase totals =	$856.88		$932.5516	$932.54	$932.55	$932.60