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	$176.30	12.471%	$198.2864	$198.29	$198.30	$198.30
Purchase #2	$19.63	4.642%	$20.5412	$20.54	$20.55	$20.50
Purchase #3	$135.38	4.473%	$141.4355	$141.44	$141.45	$141.40
Purchase #4	$35.88	5.628%	$37.8993	$37.90	$37.90	$37.90
Purchase #5	$86.44	4.357%	$90.2062	$90.21	$90.20	$90.20
Purchase #6	$66.87	12.757%	$75.4006	$75.40	$75.40	$75.40
Purchase #7	$37.84	11.627%	$42.2397	$42.24	$42.25	$42.20
7 purchase totals =	$558.34		$606.0089	$606.02	$606.05	$605.90