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	$79.61	12.481%	$89.5461	$89.55	$89.55	$89.50
Purchase #2	$17.98	5.130%	$18.9024	$18.90	$18.90	$18.90
Purchase #3	$245.56	9.134%	$267.9895	$267.99	$268.00	$268.00
Purchase #4	$102.88	8.207%	$111.3234	$111.32	$111.30	$111.30
Purchase #5	$168.56	8.447%	$182.7983	$182.80	$182.80	$182.80
Purchase #6	$94.34	4.849%	$98.9145	$98.91	$98.90	$98.90
Purchase #7	$125.32	10.438%	$138.4009	$138.40	$138.40	$138.40
7 purchase totals =	$834.25		$907.8751	$907.87	$907.85	$907.80