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	$55.60	6.145%	$59.0166	$59.02	$59.00	$59.00
Purchase #2	$104.58	12.200%	$117.3388	$117.34	$117.35	$117.30
Purchase #3	$72.96	10.330%	$80.4968	$80.50	$80.50	$80.50
Purchase #4	$91.67	6.865%	$97.9631	$97.96	$97.95	$98.00
Purchase #5	$45.52	11.689%	$50.8408	$50.84	$50.85	$50.80
Purchase #6	$117.29	12.143%	$131.5325	$131.53	$131.55	$131.50
Purchase #7	$213.75	7.354%	$229.4692	$229.47	$229.45	$229.50
7 purchase totals =	$701.37		$766.6578	$766.66	$766.65	$766.60