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	$249.32	6.560%	$265.6754	$265.68	$265.70	$265.70
Purchase #2	$106.31	12.441%	$119.536	$119.54	$119.55	$119.50
Purchase #3	$115.63	5.113%	$121.5422	$121.54	$121.55	$121.50
Purchase #4	$5.62	5.689%	$5.9397	$5.94	$5.95	$5.90
Purchase #5	$63.83	6.270%	$67.8321	$67.83	$67.85	$67.80
Purchase #6	$186.50	12.219%	$209.2884	$209.29	$209.30	$209.30
Purchase #7	$57.50	3.848%	$59.7126	$59.71	$59.70	$59.70
7 purchase totals =	$784.71		$849.5264	$849.53	$849.60	$849.40