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	$235.76	6.406%	$250.8628	$250.86	$250.85	$250.90
Purchase #2	$211.95	10.306%	$233.7936	$233.79	$233.80	$233.80
Purchase #3	$153.73	7.213%	$164.8185	$164.82	$164.80	$164.80
Purchase #4	$247.90	13.145%	$280.4865	$280.49	$280.50	$280.50
Purchase #5	$157.69	11.574%	$175.941	$175.94	$175.95	$175.90
Purchase #6	$232.64	7.171%	$249.3226	$249.32	$249.30	$249.30
Purchase #7	$141.59	7.599%	$152.3494	$152.35	$152.35	$152.30
7 purchase totals =	$1,381.26		$1,507.5744	$1,507.57	$1,507.55	$1,507.50