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	$29.88	12.737%	$33.6858	$33.69	$33.70	$33.70
Purchase #2	$229.88	7.228%	$246.4957	$246.50	$246.50	$246.50
Purchase #3	$40.96	5.122%	$43.058	$43.06	$43.05	$43.10
Purchase #4	$91.33	11.473%	$101.8083	$101.81	$101.80	$101.80
Purchase #5	$167.47	6.443%	$178.2601	$178.26	$178.25	$178.30
Purchase #6	$34.80	13.460%	$39.4841	$39.48	$39.50	$39.50
Purchase #7	$211.89	7.401%	$227.572	$227.57	$227.55	$227.60
7 purchase totals =	$806.21		$870.3640	$870.37	$870.35	$870.50