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	$239.65	9.104%	$261.4677	$261.47	$261.45	$261.50
Purchase #2	$38.81	9.402%	$42.4589	$42.46	$42.45	$42.50
Purchase #3	$196.72	10.807%	$217.9795	$217.98	$218.00	$218.00
Purchase #4	$235.90	6.164%	$250.4409	$250.44	$250.45	$250.40
Purchase #5	$15.93	10.842%	$17.6571	$17.66	$17.65	$17.70
Purchase #6	$232.33	7.560%	$249.8941	$249.89	$249.90	$249.90
Purchase #7	$220.30	8.173%	$238.3051	$238.31	$238.30	$238.30
7 purchase totals =	$1,179.64		$1,278.2033	$1,278.21	$1,278.20	$1,278.30