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	$203.62	9.677%	$223.3243	$223.32	$223.30	$223.30
Purchase #2	$90.77	3.298%	$93.7636	$93.76	$93.75	$93.80
Purchase #3	$80.38	3.129%	$82.8951	$82.90	$82.90	$82.90
Purchase #4	$68.44	6.571%	$72.9372	$72.94	$72.95	$72.90
Purchase #5	$94.86	11.279%	$105.5593	$105.56	$105.55	$105.60
Purchase #6	$133.32	8.769%	$145.0108	$145.01	$145.00	$145.00
Purchase #7	$159.78	9.556%	$175.0486	$175.05	$175.05	$175.00
7 purchase totals =	$831.17		$898.5389	$898.54	$898.50	$898.50