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	$168.62	11.465%	$187.9523	$187.95	$187.95	$188.00
Purchase #2	$221.56	12.428%	$249.0955	$249.10	$249.10	$249.10
Purchase #3	$186.55	5.566%	$196.9334	$196.93	$196.95	$196.90
Purchase #4	$40.73	4.168%	$42.4276	$42.43	$42.45	$42.40
Purchase #5	$77.55	3.166%	$80.0052	$80.01	$80.00	$80.00
Purchase #6	$81.56	13.220%	$92.3422	$92.34	$92.35	$92.30
Purchase #7	$31.50	3.284%	$32.5345	$32.53	$32.55	$32.50
7 purchase totals =	$808.07		$881.2907	$881.29	$881.35	$881.20