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	$175.65	9.190%	$191.7922	$191.79	$191.80	$191.80
Purchase #2	$26.90	6.531%	$28.6568	$28.66	$28.65	$28.70
Purchase #3	$219.33	7.358%	$235.4683	$235.47	$235.45	$235.50
Purchase #4	$67.91	5.333%	$71.5316	$71.53	$71.55	$71.50
Purchase #5	$99.27	12.604%	$111.782	$111.78	$111.80	$111.80
Purchase #6	$36.83	10.357%	$40.6445	$40.64	$40.65	$40.60
Purchase #7	$241.59	7.547%	$259.8228	$259.82	$259.80	$259.80
7 purchase totals =	$867.48		$939.6982	$939.69	$939.70	$939.70