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	$179.55	4.858%	$188.2725	$188.27	$188.25	$188.30
Purchase #2	$43.98	8.731%	$47.8199	$47.82	$47.80	$47.80
Purchase #3	$201.94	10.800%	$223.7495	$223.75	$223.75	$223.70
Purchase #4	$81.25	5.121%	$85.4108	$85.41	$85.40	$85.40
Purchase #5	$186.47	12.232%	$209.279	$209.28	$209.30	$209.30
Purchase #6	$130.47	4.553%	$136.4103	$136.41	$136.40	$136.40
Purchase #7	$92.85	8.164%	$100.4303	$100.43	$100.45	$100.40
7 purchase totals =	$916.51		$991.3723	$991.37	$991.35	$991.30