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	$137.34	6.671%	$146.502	$146.50	$146.50	$146.50
Purchase #2	$18.32	8.710%	$19.9157	$19.92	$19.90	$19.90
Purchase #3	$243.54	10.874%	$270.0225	$270.02	$270.00	$270.00
Purchase #4	$71.35	3.511%	$73.8551	$73.86	$73.85	$73.90
Purchase #5	$247.29	8.190%	$267.5431	$267.54	$267.55	$267.50
Purchase #6	$131.82	12.171%	$147.8638	$147.86	$147.85	$147.90
Purchase #7	$55.44	12.148%	$62.1749	$62.17	$62.15	$62.20
7 purchase totals =	$905.10		$987.8771	$987.87	$987.80	$987.90