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	$61.80	8.610%	$67.121	$67.12	$67.10	$67.10
Purchase #2	$220.43	10.636%	$243.8749	$243.87	$243.85	$243.90
Purchase #3	$63.63	8.238%	$68.8718	$68.87	$68.85	$68.90
Purchase #4	$79.34	13.350%	$89.9319	$89.93	$89.95	$89.90
Purchase #5	$169.25	7.258%	$181.5342	$181.53	$181.55	$181.50
Purchase #6	$127.58	11.496%	$142.2466	$142.25	$142.25	$142.20
Purchase #7	$39.48	11.445%	$43.9985	$44.00	$44.00	$44.00
7 purchase totals =	$761.51		$837.5789	$837.57	$837.55	$837.50