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	$54.77	7.774%	$59.0278	$59.03	$59.05	$59.00
Purchase #2	$127.66	6.758%	$136.2873	$136.29	$136.30	$136.30
Purchase #3	$52.55	3.769%	$54.5306	$54.53	$54.55	$54.50
Purchase #4	$50.93	3.775%	$52.8526	$52.85	$52.85	$52.90
Purchase #5	$114.91	12.120%	$128.8371	$128.84	$128.85	$128.80
Purchase #6	$246.99	10.843%	$273.7711	$273.77	$273.75	$273.80
Purchase #7	$105.41	9.115%	$115.0181	$115.02	$115.00	$115.00
7 purchase totals =	$753.22		$820.3246	$820.33	$820.35	$820.30