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	$155.53	6.626%	$165.8354	$165.84	$165.85	$165.80
Purchase #2	$56.34	11.511%	$62.8253	$62.83	$62.85	$62.80
Purchase #3	$35.41	6.455%	$37.6957	$37.70	$37.70	$37.70
Purchase #4	$77.76	5.601%	$82.1153	$82.12	$82.10	$82.10
Purchase #5	$116.94	10.659%	$129.4046	$129.40	$129.40	$129.40
Purchase #6	$76.33	13.821%	$86.8796	$86.88	$86.90	$86.90
Purchase #7	$97.48	12.780%	$109.9379	$109.94	$109.95	$109.90
7 purchase totals =	$615.79		$674.6938	$674.71	$674.75	$674.60