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	$111.85	7.550%	$120.2947	$120.29	$120.30	$120.30
Purchase #2	$184.41	6.751%	$196.8595	$196.86	$196.85	$196.90
Purchase #3	$140.53	3.160%	$144.9707	$144.97	$144.95	$145.00
Purchase #4	$79.31	7.123%	$84.9593	$84.96	$84.95	$85.00
Purchase #5	$62.33	10.533%	$68.8952	$68.90	$68.90	$68.90
Purchase #6	$45.28	13.740%	$51.5015	$51.50	$51.50	$51.50
Purchase #7	$216.55	4.340%	$225.9483	$225.95	$225.95	$225.90
7 purchase totals =	$840.26		$893.4292	$893.43	$893.40	$893.50