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	$185.94	13.300%	$210.67	$210.67	$210.65	$210.70
Purchase #2	$194.67	10.618%	$215.3401	$215.34	$215.35	$215.30
Purchase #3	$156.96	11.177%	$174.5034	$174.50	$174.50	$174.50
Purchase #4	$129.36	9.427%	$141.5548	$141.55	$141.55	$141.60
Purchase #5	$34.33	4.303%	$35.8072	$35.81	$35.80	$35.80
Purchase #6	$82.91	10.835%	$91.8933	$91.89	$91.90	$91.90
Purchase #7	$249.61	5.579%	$263.5357	$263.54	$263.55	$263.50
7 purchase totals =	$1,033.78		$1,133.3045	$1,133.30	$1,133.30	$1,133.30