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	$113.88	8.119%	$123.1259	$123.13	$123.15	$123.10
Purchase #2	$55.89	10.600%	$61.8143	$61.81	$61.80	$61.80
Purchase #3	$127.56	9.839%	$140.1106	$140.11	$140.10	$140.10
Purchase #4	$100.46	10.579%	$111.0877	$111.09	$111.10	$111.10
Purchase #5	$216.26	12.783%	$243.9045	$243.90	$243.90	$243.90
Purchase #6	$170.99	9.276%	$186.851	$186.85	$186.85	$186.90
Purchase #7	$33.83	9.175%	$36.9339	$36.93	$36.95	$36.90
7 purchase totals =	$818.87		$903.8279	$903.82	$903.85	$903.80