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	$73.34	6.848%	$78.3623	$78.36	$78.35	$78.40
Purchase #2	$120.34	9.562%	$131.8469	$131.85	$131.85	$131.80
Purchase #3	$224.79	6.206%	$238.7405	$238.74	$238.75	$238.70
Purchase #4	$60.92	8.218%	$65.9264	$65.93	$65.95	$65.90
Purchase #5	$185.84	7.734%	$200.2129	$200.21	$200.20	$200.20
Purchase #6	$148.41	11.767%	$165.8734	$165.87	$165.85	$165.90
Purchase #7	$220.85	11.308%	$245.8237	$245.82	$245.80	$245.80
7 purchase totals =	$1,034.49		$1,126.7861	$1,126.78	$1,126.75	$1,126.70