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	$121.71	8.227%	$131.7231	$131.72	$131.70	$131.70
Purchase #2	$41.59	6.507%	$44.2963	$44.30	$44.30	$44.30
Purchase #3	$199.79	6.219%	$212.2149	$212.21	$212.20	$212.20
Purchase #4	$47.87	11.576%	$53.4114	$53.41	$53.40	$53.40
Purchase #5	$238.30	4.851%	$249.8599	$249.86	$249.85	$249.90
Purchase #6	$208.27	12.595%	$234.5016	$234.50	$234.50	$234.50
Purchase #7	$125.76	4.398%	$131.2909	$131.29	$131.30	$131.30
7 purchase totals =	$983.29		$1,057.2981	$1,057.29	$1,057.25	$1,057.30