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	$103.97	13.805%	$118.3231	$118.32	$118.30	$118.30
Purchase #2	$133.37	3.403%	$137.9086	$137.91	$137.90	$137.90
Purchase #3	$189.36	4.270%	$197.4457	$197.45	$197.45	$197.40
Purchase #4	$174.40	12.417%	$196.0552	$196.06	$196.05	$196.10
Purchase #5	$218.53	3.217%	$225.5601	$225.56	$225.55	$225.60
Purchase #6	$86.34	3.225%	$89.1245	$89.12	$89.10	$89.10
Purchase #7	$40.47	5.837%	$42.8322	$42.83	$42.85	$42.80
7 purchase totals =	$946.44		$1,007.2494	$1,007.25	$1,007.20	$1,007.20