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	$96.27	4.714%	$100.8082	$100.81	$100.80	$100.80
Purchase #2	$33.55	6.107%	$35.5989	$35.60	$35.60	$35.60
Purchase #3	$215.74	9.646%	$236.5503	$236.55	$236.55	$236.60
Purchase #4	$201.56	3.343%	$208.2982	$208.30	$208.30	$208.30
Purchase #5	$161.87	3.103%	$166.8928	$166.89	$166.90	$166.90
Purchase #6	$232.57	4.205%	$242.3496	$242.35	$242.35	$242.30
Purchase #7	$149.86	11.659%	$167.3322	$167.33	$167.35	$167.30
7 purchase totals =	$1,091.42		$1,157.8302	$1,157.83	$1,157.85	$1,157.80