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	$57.63	10.754%	$63.8275	$63.83	$63.85	$63.80
Purchase #2	$131.57	7.235%	$141.0891	$141.09	$141.10	$141.10
Purchase #3	$196.65	11.300%	$218.8715	$218.87	$218.85	$218.90
Purchase #4	$37.55	12.764%	$42.3429	$42.34	$42.35	$42.30
Purchase #5	$136.58	6.818%	$145.892	$145.89	$145.90	$145.90
Purchase #6	$168.65	3.582%	$174.691	$174.69	$174.70	$174.70
Purchase #7	$124.64	7.774%	$134.3295	$134.33	$134.35	$134.30
7 purchase totals =	$853.27		$921.0435	$921.04	$921.10	$921.00