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	$135.86	10.678%	$150.3671	$150.37	$150.35	$150.40
Purchase #2	$219.55	12.632%	$247.2836	$247.28	$247.30	$247.30
Purchase #3	$164.84	13.430%	$186.978	$186.98	$187.00	$187.00
Purchase #4	$160.53	4.107%	$167.123	$167.12	$167.10	$167.10
Purchase #5	$194.90	10.800%	$215.9492	$215.95	$215.95	$215.90
Purchase #6	$112.48	10.581%	$124.3815	$124.38	$124.40	$124.40
Purchase #7	$39.93	6.362%	$42.4703	$42.47	$42.45	$42.50
7 purchase totals =	$1,028.09		$1,134.5527	$1,134.55	$1,134.55	$1,134.60