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	$216.67	5.400%	$228.3702	$228.37	$228.35	$228.40
Purchase #2	$31.74	11.861%	$35.5047	$35.50	$35.50	$35.50
Purchase #3	$206.60	12.755%	$232.9518	$232.95	$232.95	$233.00
Purchase #4	$117.59	11.736%	$131.3904	$131.39	$131.40	$131.40
Purchase #5	$113.43	9.177%	$123.8395	$123.84	$123.85	$123.80
Purchase #6	$65.89	10.649%	$72.9066	$72.91	$72.90	$72.90
Purchase #7	$84.54	9.824%	$92.8452	$92.85	$92.85	$92.80
7 purchase totals =	$836.46		$917.8084	$917.81	$917.80	$917.80