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	$165.53	13.485%	$187.8517	$187.85	$187.85	$187.90
Purchase #2	$71.75	12.115%	$80.4425	$80.44	$80.45	$80.40
Purchase #3	$134.85	8.299%	$146.0412	$146.04	$146.05	$146.00
Purchase #4	$185.71	7.638%	$199.8945	$199.89	$199.90	$199.90
Purchase #5	$107.50	11.526%	$119.8905	$119.89	$119.90	$119.90
Purchase #6	$213.72	9.663%	$234.3718	$234.37	$234.35	$234.40
Purchase #7	$66.38	7.425%	$71.3087	$71.31	$71.30	$71.30
7 purchase totals =	$945.44		$1,039.8009	$1,039.79	$1,039.80	$1,039.80