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	$61.90	9.708%	$67.9093	$67.91	$67.90	$67.90
Purchase #2	$243.47	12.374%	$273.597	$273.60	$273.60	$273.60
Purchase #3	$201.91	7.270%	$216.5889	$216.59	$216.60	$216.60
Purchase #4	$39.54	5.673%	$41.7831	$41.78	$41.80	$41.80
Purchase #5	$92.54	10.596%	$102.3455	$102.35	$102.35	$102.30
Purchase #6	$59.36	13.609%	$67.4383	$67.44	$67.45	$67.40
Purchase #7	$72.33	12.685%	$81.5051	$81.51	$81.50	$81.50
7 purchase totals =	$771.05		$851.1672	$851.18	$851.20	$851.10