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	$116.49	12.731%	$131.3203	$131.32	$131.30	$131.30
Purchase #2	$78.87	9.865%	$86.6505	$86.65	$86.65	$86.70
Purchase #3	$57.61	9.790%	$63.25	$63.25	$63.25	$63.30
Purchase #4	$240.40	11.180%	$267.2767	$267.28	$267.30	$267.30
Purchase #5	$77.48	13.468%	$87.915	$87.92	$87.90	$87.90
Purchase #6	$98.55	12.788%	$111.1526	$111.15	$111.15	$111.20
Purchase #7	$115.26	7.265%	$123.6336	$123.63	$123.65	$123.60
7 purchase totals =	$784.66		$871.1987	$871.20	$871.20	$871.30