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	$28.69	8.416%	$31.1046	$31.10	$31.10	$31.10
Purchase #2	$145.69	3.419%	$150.6711	$150.67	$150.65	$150.70
Purchase #3	$167.90	7.423%	$180.3632	$180.36	$180.35	$180.40
Purchase #4	$172.81	13.343%	$195.868	$195.87	$195.85	$195.90
Purchase #5	$143.85	7.502%	$154.6416	$154.64	$154.65	$154.60
Purchase #6	$63.65	13.663%	$72.3465	$72.35	$72.35	$72.30
Purchase #7	$40.29	12.519%	$45.3339	$45.33	$45.35	$45.30
7 purchase totals =	$762.88		$830.3289	$830.32	$830.30	$830.30