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	$53.69	8.802%	$58.4158	$58.42	$58.40	$58.40
Purchase #2	$78.79	5.119%	$82.8233	$82.82	$82.80	$82.80
Purchase #3	$201.57	12.761%	$227.2923	$227.29	$227.30	$227.30
Purchase #4	$228.73	13.623%	$259.8899	$259.89	$259.90	$259.90
Purchase #5	$48.70	7.758%	$52.4781	$52.48	$52.50	$52.50
Purchase #6	$181.74	7.189%	$194.8053	$194.81	$194.80	$194.80
Purchase #7	$243.47	12.713%	$274.4223	$274.42	$274.40	$274.40
7 purchase totals =	$1,036.69		$1,150.1270	$1,150.13	$1,150.10	$1,150.10