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	$24.77	8.304%	$26.8269	$26.83	$26.85	$26.80
Purchase #2	$86.57	9.782%	$95.0383	$95.04	$95.05	$95.00
Purchase #3	$171.43	6.453%	$182.4924	$182.49	$182.50	$182.50
Purchase #4	$202.90	9.651%	$222.4819	$222.48	$222.50	$222.50
Purchase #5	$30.65	7.321%	$32.8939	$32.89	$32.90	$32.90
Purchase #6	$65.46	12.369%	$73.5567	$73.56	$73.55	$73.60
Purchase #7	$128.82	6.869%	$137.6686	$137.67	$137.65	$137.70
7 purchase totals =	$710.60		$770.9587	$770.96	$771.00	$771.00