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	$48.60	4.684%	$50.8764	$50.88	$50.90	$50.90
Purchase #2	$13.30	11.619%	$14.8453	$14.85	$14.85	$14.80
Purchase #3	$162.83	12.319%	$182.889	$182.89	$182.90	$182.90
Purchase #4	$45.94	10.427%	$50.7302	$50.73	$50.75	$50.70
Purchase #5	$178.98	5.389%	$188.6252	$188.63	$188.65	$188.60
Purchase #6	$98.33	12.844%	$110.9595	$110.96	$110.95	$111.00
Purchase #7	$37.55	11.676%	$41.9343	$41.93	$41.95	$41.90
7 purchase totals =	$585.53		$640.8599	$640.87	$640.95	$640.80