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	$28.63	9.117%	$31.2402	$31.24	$31.25	$31.20
Purchase #2	$30.28	3.781%	$31.4249	$31.42	$31.40	$31.40
Purchase #3	$172.48	12.323%	$193.7347	$193.73	$193.75	$193.70
Purchase #4	$66.64	8.498%	$72.3031	$72.30	$72.30	$72.30
Purchase #5	$184.57	6.681%	$196.9011	$196.90	$196.90	$196.90
Purchase #6	$113.98	4.584%	$119.2048	$119.20	$119.20	$119.20
Purchase #7	$73.66	6.347%	$78.3352	$78.34	$78.35	$78.30
7 purchase totals =	$670.24		$723.1440	$723.13	$723.15	$723.00