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	$42.74	6.523%	$45.5279	$45.53	$45.55	$45.50
Purchase #2	$114.60	7.432%	$123.1171	$123.12	$123.10	$123.10
Purchase #3	$238.79	9.116%	$260.5581	$260.56	$260.55	$260.60
Purchase #4	$89.86	9.595%	$98.4821	$98.48	$98.50	$98.50
Purchase #5	$169.31	11.486%	$188.7569	$188.76	$188.75	$188.80
Purchase #6	$198.73	11.853%	$222.2855	$222.29	$222.30	$222.30
Purchase #7	$121.29	11.803%	$135.6059	$135.61	$135.60	$135.60
7 purchase totals =	$975.32		$1,074.3335	$1,074.35	$1,074.35	$1,074.40