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	$35.41	12.401%	$39.8012	$39.80	$39.80	$39.80
Purchase #2	$154.88	8.800%	$168.5094	$168.51	$168.50	$168.50
Purchase #3	$161.83	12.629%	$182.2675	$182.27	$182.25	$182.30
Purchase #4	$92.75	7.700%	$99.8918	$99.89	$99.90	$99.90
Purchase #5	$25.69	3.382%	$26.5588	$26.56	$26.55	$26.60
Purchase #6	$243.54	6.870%	$260.2712	$260.27	$260.25	$260.30
Purchase #7	$45.84	6.643%	$48.8852	$48.89	$48.90	$48.90
7 purchase totals =	$759.94		$826.1851	$826.19	$826.15	$826.30