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	$229.51	3.810%	$238.2543	$238.25	$238.25	$238.30
Purchase #2	$74.99	4.498%	$78.3631	$78.36	$78.35	$78.40
Purchase #3	$243.27	12.586%	$273.888	$273.89	$273.90	$273.90
Purchase #4	$212.67	9.726%	$233.3543	$233.35	$233.35	$233.40
Purchase #5	$190.83	3.799%	$198.0796	$198.08	$198.10	$198.10
Purchase #6	$190.31	13.711%	$216.4034	$216.40	$216.40	$216.40
Purchase #7	$71.76	6.409%	$76.3591	$76.36	$76.35	$76.40
7 purchase totals =	$1,213.34		$1,314.7018	$1,314.69	$1,314.70	$1,314.90