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	$102.78	10.136%	$113.1978	$113.20	$113.20	$113.20
Purchase #2	$31.90	12.237%	$35.8036	$35.80	$35.80	$35.80
Purchase #3	$198.66	13.622%	$225.7215	$225.72	$225.70	$225.70
Purchase #4	$185.94	10.697%	$205.83	$205.83	$205.85	$205.80
Purchase #5	$133.33	12.134%	$149.5083	$149.51	$149.50	$149.50
Purchase #6	$52.34	6.815%	$55.907	$55.91	$55.90	$55.90
Purchase #7	$240.27	10.541%	$265.5969	$265.60	$265.60	$265.60
7 purchase totals =	$945.22		$1,051.5651	$1,051.57	$1,051.55	$1,051.50