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	$240.76	6.138%	$255.5378	$255.54	$255.55	$255.50
Purchase #2	$111.63	5.814%	$118.1202	$118.12	$118.10	$118.10
Purchase #3	$140.79	8.604%	$152.9036	$152.90	$152.90	$152.90
Purchase #4	$75.56	6.521%	$80.4873	$80.49	$80.50	$80.50
Purchase #5	$51.96	6.477%	$55.3254	$55.33	$55.35	$55.30
Purchase #6	$212.71	11.208%	$236.5505	$236.55	$236.55	$236.60
Purchase #7	$103.90	9.639%	$113.9149	$113.91	$113.90	$113.90
7 purchase totals =	$937.31		$1,012.8397	$1,012.84	$1,012.85	$1,012.80