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	$125.36	8.286%	$135.7473	$135.75	$135.75	$135.70
Purchase #2	$176.54	8.663%	$191.8337	$191.83	$191.85	$191.80
Purchase #3	$237.57	5.589%	$250.8478	$250.85	$250.85	$250.80
Purchase #4	$5.51	9.185%	$6.0161	$6.02	$6.00	$6.00
Purchase #5	$189.43	3.510%	$196.079	$196.08	$196.10	$196.10
Purchase #6	$150.71	7.800%	$162.4654	$162.47	$162.45	$162.50
Purchase #7	$173.46	8.449%	$188.1156	$188.12	$188.10	$188.10
7 purchase totals =	$1,058.58		$1,131.1049	$1,131.12	$1,131.10	$1,131.00