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	$193.78	12.780%	$218.5451	$218.55	$218.55	$218.50
Purchase #2	$67.79	6.659%	$72.3041	$72.30	$72.30	$72.30
Purchase #3	$27.58	13.124%	$31.1996	$31.20	$31.20	$31.20
Purchase #4	$124.27	6.133%	$131.8915	$131.89	$131.90	$131.90
Purchase #5	$119.89	8.411%	$129.9739	$129.97	$129.95	$130.00
Purchase #6	$241.76	8.695%	$262.781	$262.78	$262.80	$262.80
Purchase #7	$77.43	6.368%	$82.3607	$82.36	$82.35	$82.40
7 purchase totals =	$852.50		$929.0559	$929.05	$929.05	$929.10