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	$207.78	6.626%	$221.5475	$221.55	$221.55	$221.50
Purchase #2	$115.44	7.710%	$124.3404	$124.34	$124.35	$124.30
Purchase #3	$105.36	4.360%	$109.9537	$109.95	$109.95	$110.00
Purchase #4	$78.38	4.830%	$82.1658	$82.17	$82.15	$82.20
Purchase #5	$84.72	7.808%	$91.3349	$91.33	$91.35	$91.30
Purchase #6	$249.37	12.601%	$280.7931	$280.79	$280.80	$280.80
Purchase #7	$181.72	4.740%	$190.3335	$190.33	$190.35	$190.30
7 purchase totals =	$1,022.77		$1,100.4689	$1,100.46	$1,100.50	$1,100.40