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	$79.81	12.360%	$89.6745	$89.67	$89.65	$89.70
Purchase #2	$215.56	4.229%	$224.676	$224.68	$224.70	$224.70
Purchase #3	$53.82	10.621%	$59.5362	$59.54	$59.55	$59.50
Purchase #4	$91.67	11.874%	$102.5549	$102.55	$102.55	$102.60
Purchase #5	$80.90	5.322%	$85.2055	$85.21	$85.20	$85.20
Purchase #6	$175.30	4.127%	$182.5346	$182.53	$182.55	$182.50
Purchase #7	$235.38	12.860%	$265.6499	$265.65	$265.65	$265.60
7 purchase totals =	$932.44		$1,009.8316	$1,009.83	$1,009.85	$1,009.80