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	$100.92	11.438%	$112.4632	$112.46	$112.45	$112.50
Purchase #2	$39.90	3.782%	$41.409	$41.41	$41.40	$41.40
Purchase #3	$14.86	3.181%	$15.3327	$15.33	$15.35	$15.30
Purchase #4	$40.83	11.454%	$45.5067	$45.51	$45.50	$45.50
Purchase #5	$208.50	11.713%	$232.9216	$232.92	$232.90	$232.90
Purchase #6	$193.40	11.245%	$215.1478	$215.15	$215.15	$215.10
Purchase #7	$90.61	7.629%	$97.5226	$97.52	$97.50	$97.50
7 purchase totals =	$689.02		$760.3036	$760.30	$760.25	$760.20