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	$140.69	12.149%	$157.7824	$157.78	$157.80	$157.80
Purchase #2	$33.66	7.666%	$36.2404	$36.24	$36.25	$36.20
Purchase #3	$136.59	5.505%	$144.1093	$144.11	$144.10	$144.10
Purchase #4	$88.90	11.767%	$99.3609	$99.36	$99.35	$99.40
Purchase #5	$84.30	6.134%	$89.471	$89.47	$89.45	$89.50
Purchase #6	$59.86	12.811%	$67.5287	$67.53	$67.55	$67.50
Purchase #7	$43.78	3.797%	$45.4423	$45.44	$45.45	$45.40
7 purchase totals =	$587.78		$639.9350	$639.93	$639.95	$639.90