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	$27.73	12.864%	$31.2972	$31.30	$31.30	$31.30
Purchase #2	$196.92	9.589%	$215.8027	$215.80	$215.80	$215.80
Purchase #3	$170.48	9.116%	$186.021	$186.02	$186.00	$186.00
Purchase #4	$42.25	12.390%	$47.4848	$47.48	$47.50	$47.50
Purchase #5	$139.72	12.333%	$156.9517	$156.95	$156.95	$157.00
Purchase #6	$145.76	13.803%	$165.8793	$165.88	$165.90	$165.90
Purchase #7	$68.88	5.145%	$72.4239	$72.42	$72.40	$72.40
7 purchase totals =	$791.74		$875.8606	$875.85	$875.85	$875.90