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	$7.53	6.380%	$8.0104	$8.01	$8.00	$8.00
Purchase #2	$23.38	5.591%	$24.6872	$24.69	$24.70	$24.70
Purchase #3	$144.44	4.645%	$151.1492	$151.15	$151.15	$151.10
Purchase #4	$133.78	12.341%	$150.2898	$150.29	$150.30	$150.30
Purchase #5	$79.36	13.676%	$90.2133	$90.21	$90.20	$90.20
Purchase #6	$37.30	12.552%	$41.9819	$41.98	$42.00	$42.00
Purchase #7	$159.55	9.304%	$174.3945	$174.39	$174.40	$174.40
7 purchase totals =	$585.34		$640.7263	$640.72	$640.75	$640.70