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	$42.96	11.528%	$47.9124	$47.91	$47.90	$47.90
Purchase #2	$237.33	10.146%	$261.4095	$261.41	$261.40	$261.40
Purchase #3	$208.61	10.488%	$230.489	$230.49	$230.50	$230.50
Purchase #4	$75.43	12.794%	$85.0805	$85.08	$85.10	$85.10
Purchase #5	$42.36	8.199%	$45.8331	$45.83	$45.85	$45.80
Purchase #6	$69.38	5.430%	$73.1473	$73.15	$73.15	$73.10
Purchase #7	$78.56	6.487%	$83.6562	$83.66	$83.65	$83.70
7 purchase totals =	$754.63		$827.5280	$827.53	$827.55	$827.50