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	$154.86	10.225%	$170.6944	$170.69	$170.70	$170.70
Purchase #2	$39.30	6.364%	$41.8011	$41.80	$41.80	$41.80
Purchase #3	$57.99	3.276%	$59.8898	$59.89	$59.90	$59.90
Purchase #4	$179.88	10.745%	$199.2081	$199.21	$199.20	$199.20
Purchase #5	$42.34	11.776%	$47.326	$47.33	$47.35	$47.30
Purchase #6	$198.35	6.665%	$211.57	$211.57	$211.55	$211.60
Purchase #7	$40.82	4.638%	$42.7132	$42.71	$42.70	$42.70
7 purchase totals =	$713.54		$773.2026	$773.20	$773.20	$773.20