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	$64.78	9.595%	$70.9956	$71.00	$71.00	$71.00
Purchase #2	$90.45	11.498%	$100.8499	$100.85	$100.85	$100.80
Purchase #3	$168.91	10.685%	$186.958	$186.96	$186.95	$187.00
Purchase #4	$172.51	13.761%	$196.2491	$196.25	$196.25	$196.20
Purchase #5	$89.55	9.313%	$97.8898	$97.89	$97.90	$97.90
Purchase #6	$30.51	4.161%	$31.7795	$31.78	$31.80	$31.80
Purchase #7	$236.34	8.791%	$257.1166	$257.12	$257.10	$257.10
7 purchase totals =	$853.05		$941.8385	$941.85	$941.85	$941.80