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	$177.83	6.398%	$189.2076	$189.21	$189.20	$189.20
Purchase #2	$78.86	13.502%	$89.5077	$89.51	$89.50	$89.50
Purchase #3	$28.56	13.361%	$32.3759	$32.38	$32.40	$32.40
Purchase #4	$7.44	7.794%	$8.0199	$8.02	$8.00	$8.00
Purchase #5	$142.72	12.474%	$160.5229	$160.52	$160.50	$160.50
Purchase #6	$143.53	12.874%	$162.0081	$162.01	$162.00	$162.00
Purchase #7	$59.87	13.646%	$68.0399	$68.04	$68.05	$68.00
7 purchase totals =	$638.81		$709.6820	$709.69	$709.65	$709.60