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	$187.38	8.813%	$203.8938	$203.89	$203.90	$203.90
Purchase #2	$104.42	3.614%	$108.1937	$108.19	$108.20	$108.20
Purchase #3	$45.89	9.340%	$50.1761	$50.18	$50.20	$50.20
Purchase #4	$17.77	6.134%	$18.86	$18.86	$18.85	$18.90
Purchase #5	$17.40	6.401%	$18.5138	$18.51	$18.50	$18.50
Purchase #6	$245.48	9.455%	$268.6901	$268.69	$268.70	$268.70
Purchase #7	$126.92	3.642%	$131.5424	$131.54	$131.55	$131.50
7 purchase totals =	$745.26		$799.8699	$799.86	$799.90	$799.90