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	$37.54	8.452%	$40.7129	$40.71	$40.70	$40.70
Purchase #2	$119.80	9.819%	$131.5632	$131.56	$131.55	$131.60
Purchase #3	$57.69	12.167%	$64.7091	$64.71	$64.70	$64.70
Purchase #4	$156.55	9.777%	$171.8559	$171.86	$171.85	$171.90
Purchase #5	$82.64	7.759%	$89.052	$89.05	$89.05	$89.10
Purchase #6	$231.71	11.522%	$258.4076	$258.41	$258.40	$258.40
Purchase #7	$80.97	9.181%	$88.4039	$88.40	$88.40	$88.40
7 purchase totals =	$766.90		$844.7046	$844.70	$844.65	$844.80