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	$203.74	13.778%	$231.8113	$231.81	$231.80	$231.80
Purchase #2	$25.87	6.399%	$27.5254	$27.53	$27.55	$27.50
Purchase #3	$168.38	10.417%	$185.9201	$185.92	$185.90	$185.90
Purchase #4	$164.79	10.727%	$182.467	$182.47	$182.45	$182.50
Purchase #5	$222.63	10.244%	$245.4362	$245.44	$245.45	$245.40
Purchase #6	$26.26	11.362%	$29.2437	$29.24	$29.25	$29.20
Purchase #7	$19.65	6.604%	$20.9477	$20.95	$20.95	$20.90
7 purchase totals =	$831.32		$923.3514	$923.36	$923.35	$923.20