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	$177.40	6.228%	$188.4485	$188.45	$188.45	$188.40
Purchase #2	$110.35	12.482%	$124.1239	$124.12	$124.10	$124.10
Purchase #3	$141.97	11.506%	$158.3051	$158.31	$158.30	$158.30
Purchase #4	$130.95	8.619%	$142.2366	$142.24	$142.25	$142.20
Purchase #5	$246.53	11.460%	$274.7823	$274.78	$274.80	$274.80
Purchase #6	$62.87	7.809%	$67.7795	$67.78	$67.80	$67.80
Purchase #7	$167.77	12.614%	$188.9325	$188.93	$188.95	$188.90
7 purchase totals =	$1,037.84		$1,144.6084	$1,144.61	$1,144.65	$1,144.50