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	$199.69	12.854%	$225.3582	$225.36	$225.35	$225.40
Purchase #2	$244.98	7.543%	$263.4588	$263.46	$263.45	$263.50
Purchase #3	$228.90	3.556%	$237.0397	$237.04	$237.05	$237.00
Purchase #4	$196.31	9.773%	$215.4954	$215.50	$215.50	$215.50
Purchase #5	$168.75	9.854%	$185.3786	$185.38	$185.40	$185.40
Purchase #6	$123.53	12.709%	$139.2294	$139.23	$139.25	$139.20
Purchase #7	$31.66	11.843%	$35.4095	$35.41	$35.40	$35.40
7 purchase totals =	$1,193.82		$1,301.3696	$1,301.38	$1,301.40	$1,301.40