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	$244.99	6.606%	$261.174	$261.17	$261.15	$261.20
Purchase #2	$27.32	3.735%	$28.3404	$28.34	$28.35	$28.30
Purchase #3	$80.47	12.506%	$90.5336	$90.53	$90.55	$90.50
Purchase #4	$84.89	11.850%	$94.9495	$94.95	$94.95	$94.90
Purchase #5	$90.67	8.393%	$98.2799	$98.28	$98.30	$98.30
Purchase #6	$189.55	3.346%	$195.8923	$195.89	$195.90	$195.90
Purchase #7	$40.47	11.840%	$45.2616	$45.26	$45.25	$45.30
7 purchase totals =	$758.36		$814.4313	$814.42	$814.45	$814.40