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	$170.29	9.443%	$186.3705	$186.37	$186.35	$186.40
Purchase #2	$140.96	4.349%	$147.0904	$147.09	$147.10	$147.10
Purchase #3	$85.50	5.213%	$89.9571	$89.96	$89.95	$90.00
Purchase #4	$94.28	9.626%	$103.3554	$103.36	$103.35	$103.40
Purchase #5	$37.34	12.234%	$41.9082	$41.91	$41.90	$41.90
Purchase #6	$156.35	7.729%	$168.4343	$168.43	$168.45	$168.40
Purchase #7	$154.76	9.817%	$169.9528	$169.95	$169.95	$170.00
7 purchase totals =	$839.48		$907.0687	$907.07	$907.05	$907.20