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	$65.57	11.194%	$72.9099	$72.91	$72.90	$72.90
Purchase #2	$61.52	11.591%	$68.6508	$68.65	$68.65	$68.70
Purchase #3	$177.59	6.155%	$188.5207	$188.52	$188.50	$188.50
Purchase #4	$75.73	13.398%	$85.8763	$85.88	$85.90	$85.90
Purchase #5	$117.25	6.496%	$124.8666	$124.87	$124.85	$124.90
Purchase #6	$86.29	3.207%	$89.0573	$89.06	$89.05	$89.10
Purchase #7	$195.85	13.161%	$221.6258	$221.63	$221.65	$221.60
7 purchase totals =	$779.80		$851.5074	$851.52	$851.50	$851.60